Use a 120y h150 auto tailshaft or a early bluebird tailshaft and stumpy L series 5 speed like sss stanza box or r30 skyline stumpy box.
Stanza crossmember won't fit but unpick mounts from it and stock ute one and use stanza ones on 1200 Cross member once engine is in place.
Also try to use bluebird L20b or at least sump and oil pick up off one or stanza sump and oil pick up as they are front bowl facing sump like a series.
With L20b you really need to scallop centre section out of 1200 cross member to get engine down low enough for clearance.