axle spring swap questions 88 sub to a 64 sub

[jonzcustomshop]

I am going to convert my 64 suburban 2wd to 4X4
It is not going to be a build for any kind of wheelin, just a 4X4 for winter transportation.

my donor(s) are a 88 3/4 ton suburban.
an 87 swb fleet 1/2 ton with a 4 inch lift kit.
and a 88 1/2 ton 2wd suburban.

I am only allowed to use the lift kit off the 87, the axles and frame are spoken for.

so off the 87 comes 4 shocks, steering arm, front springs and rear blocks.

off the 88 3/4 ton comes front & rear axle, brake booster , turbo 400 and transfer case, and all the assorted bracketry from the front of the frame.

so now I have 3 options at the rear, use the 3/4 ton springs and brackets, use the 1/2 ton 2wd suburban rear springs and brackets (6 leaf), or use the springs off the 87 1/2 ton fleet (5 leaf), and the brackets off either sub.+ the 4 inch blocks.

which would be the best rear option?

I am thinking of using the 2wd sub springs, thinking they are stronger than the pickup, and might work better with my early sub-(roof, seat and glass in the back)
I don't think I need to use the 3/4 rear springs, I am not going to tow anything, and the fronts are only rated 1/2 ton anyway...

2 other questions about the 88 sub... what is the lever connected to the center of the rear end that goes to the frame, and I unplugged 1 wire from the transmission -reverse light I hope? not some sort of electric lockup?
and I unplugged a dual wire from the transfer case... what does that one do?