Howdy Back Bob & ken:
We've done the motormount slot drop for years with no adverse effect. Think about it. If you can drop the engine 1/2" at the motor mounts, the rear pivot point is the trans mount- way at the back. That half inch at the front would be equal to a very small amount at the tailshaft. I doubt that the angle would change more than 1 degree. U-joints can easily compensate for that small amount.
Bob- another thought is to keep all carb to head adapters and gaskets as thin as possible. I ended up cutting my black plastic spacer to the minimum thickness needed for linkage clearance.
Adios, David