I have a t5 sitting on a crossmember from Modern Driveline in my '66. Went straight in with no problems. Importantly, it only changed the critical driveshaft angle by 0.3 of a degree so I don't get any vibration. There are other crossmembers available, including home made ones, that will drop a t5 down too low and change your driveshaft angle acceptably.
Another approach that Shaunp on here uses is to move the reinforcement rib on the tunnel and use a modified original (C4 or Top Loader) crossmember to also preserve driveshaft angle.
