Another Trany question

[tc4x4]

My Sierra 35 has the sm465 trany in it. I wanted to swap in a 5 speed trany or something, I don't know anything about what one to look for or what would go into the swap, but i am interested in it, overdrive would be nice with a manual.

So what trany would be a quick trany for the c35?

Also, would i be able to keep the bench seat?

Would i have to do any floor modification?

I know i would have to make a cross member for it.