I've never put a World Products block in a car. But I tried to put an Indy block in a car and had an experience like yours. I have 3 blocks here. One Street hemi, one mega block and a new KB. All three are different widths at the motor brackets. .600" variance between the 3. I don't know what would happen if you put 2 of those blocks in a car. I have put a 1995 hemi block in a 70 Superbird with Schmacher mounts on a wedge K-frame using Stage V valve covers. (Stage V made your valve covers for Ray Barton.) It was tight but everything fit perfect. (I think I had to use bolts instead of studs in the value covers to get them on.) I think the Schumacher mounts were one of the best fitting/performing parts of the 200 or so parts I bought to do the car. Someday I will find a set of real prints for a Hemi block and then I can tell you the problem.