I realize I am a little late to the party, but I wanted to try to help out on the radiator information before it was real old news.
Basically true. The first gens were in fact the only ones to get the curved outlet. There were some minor differences along the way (mainly thickness), but the one thing that did stay the same through the years was the height. A short rad was the same height across the board. GM never put a tall rad in a first gen. It will fit, but it is a full custom job.
Yes, 73-80 trucks used that plate type upper mounting for the tall radiators. The '81 and newer four row rads are the same as the early ones (industry number 730), the diesel/later BBC radiator being the same height, but a few inches wider. From 73-80 versus the 81 up, the only difference is the upper mounting setup. Instead of the plate, they used two individual bolt-on upper brackets that held the radiator bushings. Now, some other things changed in that timeframe. From '81 on, HDC on a small block no longer got you a four row rad like it did in earlier years. It now got you a tall three row. The short three row was still used after '81, but it no longer had an upper mounting plate. The upper mounting plate function was now handled by the shroud which had the "plate function" built into it. A tall four row radiator can be a bolt-in deal for a '81 up small block truck. You need the tall four row rad, the upper mounting brackets for a BBC/6.2L and a fan shroud from a 73-80 w/HDC and A/C.
Part of the reason this looks wrong is because the upper shroud is '81up and it is shown on an '80 down core support. This setup is one that I had thought about, but never actually tried. It is hard to tell from the pics, but it looks like the upper mounting brackets are not there. This radiator was not invented until the later '81 up core support, so mounting it in an '80 down would require some engineering especially in the shroud dept to make it look decent.The pinchweld at the top of the core support changed--on the 73-80, it was a very flat-top core support whereas the '81 up had a "ridge" at the back of the top of the core support. I have seen some pretty hack jobs of making the early plate work on the later core supports, but it really isn't too right.
I hope this helps as, generally speaking, most of the rads are the same for a given height, just different mounting early to late.
Last note for future builders: the tall four row radiators are available in aluminum (two 1' rows instead of four) in AC Delco 20978 (or equivalent). I recently purchased one in a industry number 730 box and it had a Delco/Harrison rad in the box with all of the GM markings ground off of it. I think it was under $200.00. Just some food for thought.
And somebody comes along with more knowledge than me.
I have to admit my knowledge of 81 up is very limited.
I just haven't messed with the stuff that much.







