Wow, that is convenient! :naughty:
GM makes a good set of lifters. :D You could even get away with stock LQ4 lifters. Or LS7 lifters. Or CTS-V lifters.
I just recommend new lifters cause you bought a higher mileage motor from a guy who thought it had iron heads and had a small eyebrow on a piston. It would be a shame to dump all of that time and money into a motor just to find out you trash the thing cause a lifter collapsed.