Transmission selection & associated components-vendor selection

[AB69Z]

Ready to order a T56 for my 69 Camaro project. My full DSE suspension is going in right now. I have lots of questions here. And am really looking for the expertise from this site

- do I order one from the local GM dealer (if so is there one in particular) or do I order from a vendor like Bowler?
-Bell housing GM or alternate (differences between them)
- Clutch type ? GM LS7 clutch, Pressure Plate , Flywheel, All Bolts , Pilot Bearing
- Slip Yoke
- GM Transmission mount
- Crossmember which I know is aftermarket
- Transmission Tunnel panel which is aftermarket
- Shifter
- Drive Shaft, steel or aluminum, what's the difference?
Whatever I can order from the GM dealer should be helpful to me on these parts selection