What are you using for engine mounts? You seem to be trying to solve a problem which should not exist with this swap. I have put a 350/TH400 in a '49 3100. I used a factory serpentine belt system and there is no issue with the from cross member, nor the full size HEI distributor. I used Classic Engineering engine mounts.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission