Dragonus18

I was wondering if anyone has done this shortblock swap before? I just got the Livernoise 5.0 block from a S-197 mustang put into my 2 valve and the car thumps really hard now. It sounds like the thump almost of a diesel at idle and all the way up to about 2k rpms and my engine builder says that it's 100% fine and it's just the bigger pistons. Now I believe him but I just want to see if anyone else who has done this swap has experienced the same thing? Like always, anyone's input would be greatly appreciated.