it'll work...
it works, but (there's always a problem...) when you use the manual shifter kits,you are essentially creating a manual shift thm-400...the trans will need some way to sense vacume much like the 400,to help control line pressure and shift points.unlike the 400 the 4l-80 has nothing resembling a mechanical governer.without PRECISE control of vacume in relation to throttle position,the line pressure in the 4l-80 will be hard to control...much like haveing a maladjusted TV cable on a 700-r.this can very quikly lead to a burnt trans when used in an all around street / trail rig.
The vac pump on the 6.2 will supply the vacume,but the vacume controller on the IP is not really precise enough to control vacume for the 4l-80.add that to the fact that the line pressure in the 4l is normally controlled by a solinoid,which itself is normally controlled by the tcu...and you suddenly have to mod the line pressure controller in the trans.(it's just behind the pump in the 4l-80...just a piston.)this means trans dissasembly,the apropriate kit and parts,precission reamers for the piston bores,and the skilled person to do the job/set-up/test.
The trans was designed to be used under computer control.full manual is really only a race thing.if i was using a 4l-80 exclusively off-road or at the trac,it's exactly what i would do.i'd also have a spare trans to replace the first one when i burnt it out after a few weeks.besides...a manual shift auto usually shifts hard enough to snap your neck.regardless of speed or throttle position.not fun for a daily driver.
Heres a few pics by the way.the difficulties remaining are trans lines (got to get a decent tubing bender),shift linkage(i can use the 400 linkage with a bend or two) and the TPS.turns out that the tps from a non electronic db2 will bolt to an earlier db2 with no trouble.trying to find a used one, as new is over 120$...ick.as for drive shafts,the front will have to be shorter,the rear longer.seems the np-205 is shorter and more compact than the 208.found a front shaft from an 80' suberban with a 205,that will fit perfect,just need to clearance the c/v for a little extra angle.