Picked up a 73...now need advice.

[manimal]

Been a while since I had a square, but yesterday I picked up a 1973 Cheyenne Super 20 for $400. Its a big block truck/TH400. The guy I bought it from over heated it, put water back in it and drove some more.....next day it ran, but while driving it, it stopped/died. Thats where it stayed. I was hoping it was a simple fix, but the 454 is seized.
Now on to my questions......I have a 1985 C30 parts truck with a good running 350 that I could swap out...."OR".....I have a 1998 L29 complete from a 98 Suburban 2500, I have ALL accessories,brackets, everything from a transplant.
How I got the L29 was a friend of mine is a mechanic, one of his customers had this Suburban that was making noise like a clattering sound from the engine area, so he went and purchased a take out(COMPLETE, even the harness). Had the truck towed 100 miles to my friend to do a swap. I helped him, and when we got to the torque converter, we noticed the flexplate was BROKEN...hence the noise! We did the swap and I bought the engine we pulled with everything for $150. Im 'assuming' its a good engine.(I will pull pan to inspect though)
So which one do I swap into the 73?