My concern would be that of the total distance between mounts. Although later packages used the trans mount and the 'front' engine mounts, the actual 'front' side mounts are quite far from the front of the engine, especially on an inline.
I do believe that some style of brace/strut would be required between pan rail and bottom of trans case. MotherMopar even used some on trucks/vans in the 60's-70's with 318-TF.
When I look at something of this nature, I always look to the factory to see if there is something comparable to study, afterall, they spent tens-of-millions on R&D.