I've read that there are Mono-Leaf and Multi-Leaf designs. Mono is a single leaf, and the multi is usually 4 or 5. Mine has 2. Whats going on with this? I need to get new shackles and bushings and leaf spring isolators but the stuff is leaf spring specific and I don't know if I should get mono or multi-leaf kits.

'67 model year came with mono springs.
'68 had multi-leaf, depending on model.
If yours has two leaf, I would say they were swapped or replaced sometime in the past with a non stock spring.
Different types of springs will fit, just a matter whether you want stock specs, or a higher/lower spring rate.
Most parts catalogs show correct springs by year + model. Eaton Spring has correct tables on their website. (or at least they did when I bought mine 10+ years ago)

Dang. That’s not what I was hoping to hear but thanks for the info.

So now the big question. Should I go with a 4 spring or 5 spring as a replacement? I see people putting in 5's and getting good rear ride height. I wonder if being a convertible if that will impact the leaf spring selection. It looks like I will be replacing all the perches and bolts including all the rubber stuff. Any recommendations on a kit that will solve all of this for me? Can I install a 68 setup in the 67? This may be more of a problem than I though because shipping stuff like leaf springs into Canada is expensive and takes forever these days. The "trial and error" method is not feasible at all for determining ride height.

I see that Hotchkis sells a kit that drops 1.5" from stock or 3". With the stock height looking lower than the from, why would anyone want to lower the back at all. Since I do not have stock springs in right now, I have no idea if I need them lower than stock, at stock, or above stock.

Anyone who has done this to their 67 convertible who can offer some advice would be very appreciated. Especially pics or parts.

It sounds counter-intuitive, but a greater number of leafs does not mean a stiffer spring or higher stance.
For '68, the 400 model came with 4 leaf springs. The 350 model came with 5 leaf springs.
For '67, the rearend had both rear shocks aligned. In '68 they changed to staggered shocks to eliminate wheel hop.
That's why '67 models came with one or two factory traction bars. (again, depending on model)
Different springs have different spring rates, regardless of the number of leafs.
I would recommend you have a telephone conversation with someone from Eaton Spring regarding what set-up you have, and what you are trying to do to it.
Regarding the hardware and pads, most everyone sells a kit to go along with their springs, once you decide on those.
I just found the contact info from the guy I talked to back in 2008: No idea if Mickey is still there 12 years later...

Thank you
Mickey
Phone 1-313-963-3839
Fax 1-313-963-7047
www.eatonsprings.com

Not sure you can just put multi’s on there. You need to consider the spring perches on the 67 rear. Also the lower plates are an issue because 68/69 lower plates are for staggered shocks. I’m sure it can be done but may be tricky. I’ve got a multi leaf 69 rear on my 67.

https://www.detroitspeed.com/detroit-speed-inc-mono-to-multi-leaf-conversion-kit-041101

Beware that it might give you cancer.

Removed the axle everything connected to the axle. The axle seems to be in good shape but I'll have to dig into it to be sure. May upgrade t o a posi.

The leaf springs are another story. They seem to be a Mono-leaf setup originally and it looks like someone added a second leaf to the first. I've heard that this was sometimes a dealer added thing on some convertibles. The springs are tapered: 2" in the middle and about 2.5" to 2.75" at the eyes. Also, I do not have U-Bolts or the T-Bolts connecting the perch, just 4 regular bolts per side (which are ridiculous to remove because getting a wrench or socket in there to hold the head is near impossible). In all your experience, does this jive with the typical mono-leaf setup, except of course for the added leaf-spring?

Also, what are good replacement bushings and pads to get? I've read that the urethane ones can squeak a lot. And read good things about P.S.T. stuff. Also looking at Energy Suspension, Prothane and Steele rubber products.

I basically need everything that is rubber from the transmission mount to the shackles. Does any one company sell this as a kit? I think I have the Radius Rod bushings solved, and there is some good stuff in the Ames catalogue. But almost no one puts the measurements of their products out there (serious pet peeve of mine).

Like Bob says, you have to consider the mono leaf perches. Not only are they not as deep as the multi leaf spring perch, they also don't have the hole that the center bolt sits into. When I was hunting for new springs, I saw Eaton had a 126 pound spring rate three leaf spring, mono leaf replacement that had the center bolt peened flush to fit the mono leaf perch. I was going to buy those for my 68, which has a mono leaf 69 Camaro rear, but the cost of getting them to Pender Island was out of reach. I bought five leaf springs, drilled out the center of the perch to take the center bolt and welded blocks onto the perches to extend them to fit the springs.

I'll add a pick of the perches with the hole drilled. I ground the tip off a 1/2" drill once the hole was through the perch and used it to flatten off the bottom of the hole, similar to a bottoming tap. Can't seem to find a pick of the blocks welded in.

You may be able to use the same lower plates/shock mounts.