Well, when removing engine last night outa car, I managed to bump the lower heater core tube and wouldn’t you know it, started leaking. I’ve heard not fun things about replacing these, any better with a empty engine bay? Anybody have some steps for me as to the best way to go about it? Thanks in advance!
Its a 68 400 4 Spd without AC.

Comes out from the inside of the car.

See the service manual procedure, Figure 1-10 last page.

http://thefirstgensite.com/library/68sm/hvs/hvs.html

Does having the engine out make this job any easier? Was really planning on installing new engine tonight and sounds like my new core won’t be here until Monday. I would really like to proceed with it and perhaps go for a drive this weekend, but don’t want to regret it? I would just bypass the core for the time being.

I would tackle the heater core 1st. I took advantage of the motor being out and it can really help getting the engine bay side cover off and back on.

You probably don't need a new core. Built out of heavy duty copper. Take it to a place that does core servicing and it should be done in an hour or so. They tank (clean) the core and the solder them. You have to be mindful of that core when replacing it and putting engine in. One bump and you screwed again. New is not always better.
You can install with engine in. It's just a little tighter to get in and get the nuts on. The fun stuff is taking the fender and hood off. You gotta break a few bolts to get them off.

Good luck.

X2. Its so much better to fix a good original heater core. The replacements are pretty much all poorly made and a lot more fragile than the originals.

Well, I tried the parts store route and of course, not right after waiting days for a new core. Looks to have correct bent tubes but is overall much smaller then the one I’m trying to replace and clips won’t even come close to holding it in heater box, I’ll try Ames or finding a place to resolder the one I had.

I ended up installing engine, because I was sick of waiting for a core, but I should be able to just hook the hose from Waterpump directly to the nipple on back of head and bypass heater core so I can drive it for the time being, correct?

Correct.

I can vouch that this is one component that I had to got to Ames to get the right one.

The white one is not copper and it's made in China. I would re-solder copper one and sell it if you like the Ames core. You sill get some of you $ back. Mine is 50 years original, re-soldered a couple of times. Some things you buy new, like air cleaners and oil.

You can find copper ones but just need to confirm that. I had a tube fall off and tried to re-solder it - ended up melting the fins and it was a disaster. The tubes are too close to the thin fins, and if your not an expert, you'll ruin it. I just got a new one that was copper and put it in.

Tackled this project last weekend and into the week a few nights, what a pain in the rear!! I would be just fine if I didn’t have to do that again for a long long time!

If there’s a way to do that completely from inside the car, I’d love to see it! I messed around with it for quite sometime, before finally taking the fender completely off. There’s just no way with them angled tubes on a non ac car that I could see possible. Hard to believe that was the best design they could come up with in 1968, but oh well, done now, have heat again!
Thanks for everyone’s help!

Years ago I had to fix my core on my coupe. I cut the opening in the core cover larger so I could get the angled tubes in without buggering the soldered tubes. I had to take that leaking core out at least 2 times. Make sure the core tubes do not touch the block. Not a fun job. The guy that owned my vert before me cut the inside wheel well on the passenger side so he could access the core, A/C. fan etc. I decided to leave it that way. I worked for me because the heating failed (wiring) and I had to access the fan and wiring in order to fix it. Fender and hood stays on.

Have changed the core a few times and learned more each time. Also have found different sized cores. 68 to 69 or 400 to 350. Not sure if it was the year or the size of the engine, but the housings seem to be all the same, you just need the right mounting clips and foam mounting pads. Also found that the thickness of the housing gaskets is important and will change the distance of the hose nipples from the block.
The core housing dose come out from the inside but the nuts to loosen it are on the outside of the firewall under the fender. You can save a lot of time, and having to remove the hood and fender (and risk scratching paint) by removing the inner fender to gain access. Not easy, but easier.