I too had a similar problem. The problem was that when the engine was bolted to the mount, it stressed the mount (warped it) and this caused the binding. What I did was I made sure that there were no machine marks on the crankcase that would cause the engine to not sit in correctly. I then beveled the inside edge of the mount (where the engine sits). This would allow the engine to basiclly drop in without any force applyed to the mounting bracket. What you should look for is the engine should sit flush or on top of the mounts and not push the mount outwards. You should be able to sit the engine on top on it drop right in without any problems. Let me know how it goes...
One more thing, the engine should not touch anywhere on the mount execpt the top of the lugs.