Okay, I've finally got my '84 L69 running. It is however peeing coolant out of the back. It looks like it's coming down off the oil pan. Where are the freeze plugs on these engines, and how do you change them? Sorry for the noob question, and nothing really came up on search.

 

there is a plug at the back of each cylinder bank inside the bell housing. You will need to remove the transmission and then the flywheel or flexplate (whichever trans you have), to gain access

 

As for how to change them, get a hammer and a punch, and **** the thing in it's boss. Then clamp vise-grips on it, and leverage them against the far side of the boss. Pops right out. Cl;ean it good, put some sealer around the boss and around the new plug, then using a socket big enough to fit the plug, tap it in to match the other side.
I've done hunderds of these as a professional automotive machinist. trying to get by with JB Weld does not work on this. If the leak isn't from a plug, it could be from the back of your intake manifold. The coolant passages in the heads dead-head against the earlier manifolds, and if the intake gaskets are the originals, they could have failed.
If this also isn't the problem, then suspect a cracked block. If this is the case, it has to come out, but might be salvageable, depending on what you find.