833OD into 78 D100 questions

I have a 78 short bed stepside D100 with a slant 6 and 3 on the tree. I also have an 833OD that has a longer tail shaft as well as a disassembled regular 833 that comes with a shorter A body tail shaft. I have the slant 6 bellhousing for the OD trans as well as z bar, clutch fork and a bunch of other parts.

Since it already has a 3 on the tree, is it going to be a lot easier to install than if it had an auto? Can I use the clutch and pressure plate from my 3 on the tree tranny? Will the z bar work with the OD tranny? I'm trying to find out what existing pieces I can use to make the swap easier.

There are only two different length tail shafts right? So I'm assuming the long tail shaft on the 833 OD is going to be the correct one for my truck? I'm going for mileage so I want the OD over the regular 4 speed.

Do I need a 4 speed truck floor hump or will an a body floor hump work?

Will I need to get the drive shaft shortened or will I need to find another drive shaft thats longer?

I'm kind of confused on the OD shift pattern when people start talking about the linkages being flipped upside down. Is it going to be

1......OD
|____|
2......3

or will 3rd gear be up top with OD on the bottom?

I'm sure I have a million more questions but I'm just trying to gather all the info I can before I start in on the project. Thanks.