Need a temporary motor and good 340 block

I have a '71 e-body with the original 318 that I need to take out before the crank is completely ruined(way too much end play). I was building a 416 stroker from a 340 block but one of the lifter bores is .010" over, not sure how that happens but I need to find another block. I wanted to put another 318 or 360 in the car but I don't know which one would make the best temporary motor. I know the 360s are externally balanced and the car has a 904 trans so there may be an issue there. There are several late 70's 360 in my area and an '88 318 that is supposed to have the swirl port heads and roller cam but I would have use an electric fuel pump but I have a 4bbl intake and carb that should work. The magnum motors are supposedly better but require a different intake. I have a set of TTI headers on the car that I want to put on the next motor. Any suggestions would be greatly appreciated.