[60-66 Nut]

Dan, welcome to the board. There are alot of nice folks here. The site that kizer gave you has alot of good info on the SM465 and several other transmissions.
Sounds as though your truck has the original bell housing and cross member. If so, then it should be the 168 tooth flywheel with the 3 bolt starter mounting directly to the bell housing. You can put an aluminum bell housing if you wish, but you will have to have the block mounted starter to go with it. The only reason your bell housing won't work with the SM465 is because the input flange pilot hole is too small. You can also find you a cast iron bell housing from a 68-72 GM truck with the six or V8 that will bolt right in place of yours and use the same starter. The Novak site also tells you how you can have your housing fitted to the SM465 input flange. The two bottom bolt holes on the newer SM465's will not have any threads like the older transmissions, but you can just use longer bolts with nuts and lock washers, no biggie.
As I'm sure you already know, the 327 has a 2 piece internal rear seal, so you will have to drop the pan to change it.
Your drive shaft will not work on the SM465. The 465 has a bigger rear u-joint and does not have a slip yoke, so you will need to incorporate a slip-yoke into the drive shaft. The easiest way is usually with a 2 piece drive shaft and a hanger bearing, but a good machine shop can weld a stub shaft onto your drive shaft to match a slip yoke that will fit the transmission.
And as you said, the floor pan will of course have to be modified.

Best of luck with your swap.

60-66 Nut