"What problems will I have in the physical mounting of the engine?"

With a blue-tip wrench, Sawzall, hand grinder and a MIG, you can make anything fit anything.

I'd try to modify the oil pan first, even going so far as constructing a completely new pan and pickup to clear the existing crossmember/s in the car. If I couldn't make that work, I'd gently set the engine/trans into the bay and note where the offending crossmember interferes and where there would be room to install another crossmember that would clear the motor. Install the new crossmember, then cut the old one out. Cutting the old one out first might allow the frame to tweak.

I'm sure you know all this as a veteran hot rodder, I'm just outlining it for the newer members to learn from.

"I sectioned the trans cross member to mount T-5"

That's how I do it too, using the 2 outside pieces that fit the car and the middle 3rd piece that fits the trans, then welding all of them together into a 1-piece crossmember.