Hi, I am building a 1969 400HO convertible and decided I liked the look of the T/A and wanted to do mine different than everyone else. I decided to make mine a tribute to the Paladium silver and Black Proto-types with relocated parking lights and air intakes for the breaks, functional fender extractors and functional Ram Air. Parts are all custom fabricated...

Our original engine has been placed in storage. My personal goal was to get stock power and torque for the T/A where the 1969 would not get handed it's butt by a 2011 Camaro Convertible.
We now have a 1972 400 2bolt block punched and stroked to 468 CID all forged and blueprinted, with custom ground hydraulic roller cam, ported 670 heads, 1.65 roller rockers and all that jazz. Decided to snazz it up a little with an RPM Performer Endurashine a set of high flow ceramic coated factory appearance longbranch manifolds with ceramic coating to match the endurashine look. Snazz that up with the Billet Accessories and pullies for kicks swap in an HEI and 750CFM Endurashine electric choke rejetted of course. We tuned it to 30 BTC at 1000 Idle and all in at 36 BTC 1500 Rpm. Usable power range with the intake and carb curent valve lash is 1500-6000Rpm. With an intake and carb swap, valve lash to zero we are supposed to be able to take the engine up to 7500RPM for racing but we wanted our engine daily driven street friendly.
The engine just tested on the dyno is doing a little more than I paid for at 563ftlbs of torque @ 4000RPM (increasing fast as RPM dropped on paper w a 4K cut off on the dyno, I saw 600+ on the meter but we are quoting the print out numbers only with my current carb and intake for street use and fuel efficiency). On the HP end we have a more accurate number of 520HP @ 5300 RPM. I have decided to keep true to stock with a 5800 RPM Tach althought the engine can turn faster with some quick modifications.

Although I have already considered stall, shifting and rear gears using stock RPM range and gearing I have not considered the extra HP and torque that came with this engine designer's experience at such a cheap cost to me of $6800 for long block and all porting mods and such for my provided bolt-ons. The dyno work was free and it was cool to see his bolt-ons dyno out much higher at no charge too.

Here is the deal. The transmission is a TH400, the drive shaft is stock, the rear end is a stock 12bolt posi with new upgraded innards all that I just had built. The transmission builder knew I was shooting for stock T/A performance. I did not plan to race or do holeshots at the track. This was a street build to keep the new Camaros and Vetts from rolling up on my classic and making me eat dust. Engine builder knows what is in the new stock vehicles and says with the gearing I'll be in the low to mid 10s at the track with propper rubber.

Suspension and chasis are all maxed out for any engine build I would have done with the 670 Iron Heads. Not worried about the chasis or suspension. That's a done deal. Before it all comes together and I have to start repairing things I'd like to hear from someone who has run this kind of power in the first gens. I've always restored them to stock. Never have I modded one like this. Sort of worried with the dyno #s I am seeing now!

I have a 468 in my 68 convertible but I'm not making nearly the power you are.

You didn't ask a specific question so I will just share a little. I found I had fuel starvation issue trying to use the stock 3/8 line. I'm putting in a 1/2 line with RobbMc sending unit. I'm finding it to be a huge PITA to put the 1/2 line in. I could have went with an electric pump but I tend to like the mechanical.

The other thing that is a concern to me is the chassi flex with a convertible. Just driving down a smooth road in the feeling the gap between the door and rear 1/4 is just amazing how much it changes. I have the hotchkis sub frame connectors on my wish list. I do have the belly pan on.

It doesn't sound like you should have to much to worry about with a th400 and a 12bolt rear. Unless you put on some sticky tires and take it too the track. If you did plane to do some racing you might want to upgrade to 1350 joints and at least have a heavy duty sprag installed. my .02

I assume you have subframe connectors installed right?

Post your numbers if you make it to the track someday.
I have a buddy that runs a 74 Venture with a Kauffman built motor pushing 687 HP and he turns low tens so I'd be intersted to hear what you turn.

2x!!!
With good traction, mine cracked at the left upper A pillar and the windshield would crack a 1/4" to 1/2" every time off the line.
That was with just 470 hp.

Oh ya, be sure to have a HD drive shaft made.
Stock u-joints and or shaft will break with good tration.

You did not go into detail about what the "innards" are in the rear end...a bone stock TH400 is good to about 450-475 ft lbs of torque, give or take....but a well prepped TH400 can handle over 1,000 hp. The drive shaft is usable, but I would change to a grease-less (sometimes called sealed)U-joint set up that are available through most NAPA and Car-Quest stores...most U-joints break at the internal grease passage that the Zerk fitting screws into. I have pushed a mild prepped TH350 and a 10 bolt with Richmond Gears and Moser Axles well past the 500 hp, 500 ft lbs of torque level and had them live for 100 passes down the track. It all boils down to how you are going to drive it, and what type of tire you have on it. A race slick will break parts quicker than a street tire that spins a bit first.