340 X heads advice

Im going to look at a pair of "bare" 340 X heads on Tuesday 4/9/19. What should I look for as far as problems, I not a engine guy, so I could use some advice.
I have a early 360 short block that I want to put together for my 66 B-Cuda. I bought it minus the heads. Guy kept them.
I can get a set of 3769973 heads cheap, don't know what size valves are in the 973s. I know this block had J, or X heads on it, before I bought, so I think the X heads would be the way to go.
I also have the A-904 that was hitched to the 360 block. I will turn an already installed 8 1/4 rear.
Thanks in advance
Dave