According to the OP, this situation is temporary. He plans to adapt proper frt motor mounts and gussets, which will alter the location and fitment of the driveline. I suspect the engine will sit slightly lower.
You're frame could be tweaked, but it really doesnt matter. Did you have the frt mounts bolted down while determining where the rear mounts go? Did you mount the rear frame mounts in the same place on each side of the frame, or did you have the rear crossmember attached with the frame mounts...