It seems you ran into a lot of the troubles I did. The biggest trouble I had was from living at the parts place, I was there so much they wanted me to pay rent. I apparently got my parts much cheaper in some cases spent around $600 for everything, no tools. I used various sized c-clamps and threaded rod/washers of all sizes like you. Put pistons in using coupla thin feeler gauges and LOTS of patience, that thin plastic idea sounds like a good one! Used a piece of surface plate and homemade length gauges, 6" calipers and lots of feeler gauges to set up case to rotating parts clearances. That direct plastic thrust washer commonly tears up, shop here keeps plenty in stock. Also as to the 2 slots/oil holes which MUST line up when reverse hub installed, my '98 model had 4 instead of 2. I had trouble finding correct forward/direct/coast cylinder, weeded through 4 different numbers to find the right part, some CAN be adapted as you say by varying thick or thin steels. '98 model has a different height coast piston, VERY easy to miss this and put in wrong one if kit has both as mine did. Also instead of multiple small springs, later model has one super big one to hold down coast and forward piston assy. There's a wave washer also between coast and forward clutch pack to cushion the clutch application so end of cylinder does not crack as easy. I took the time to grind out the recessed bushings until they were weak enough to deform them to remove. Used a Dremel with carbide cutter. Had trouble with aircheck on reverse cylinder leaking, piston/checkball OK. Turned out to be the seals on pump hub shaft that holds a lot of the rotating parts. Those seals real soft, need pressure to positively push them out to seal properly. They just kinda lay in the groove unlike older style iron seal rings which would seal like the dickens there. I assumed that oil pressure would seal it up on running. It must have worked as thought because trans instantly goes into all gears with a good bump and works fine. I found damage on forward clutch piston from weld BBs (F/D/C cylinder) coming loose and going around like cannon shot. I suggest anyone buying a new welded cylinder look at it very carefully and dislodge any weld BBs stuck to the part to save grief later. Changed bushings, needle bearings, plastic shims, all bonded pistons, band, pump driveshaft (you can really get raped here, one I bought cost $80 until I found one online later for $35 and got my money back!), clutches, but only a coupla steels, others fine, converter, F/D/C cylinder, direct shell, reverse/overdrive shell/sungear. Last 3 parts for exploded forward clutch from broken snap ring area. The low/intermediate and reverse/overdrive carriers both had battle damage but planetaries were good and tight so judicious use of grinder and sandpaper put them both back in a somewhat ugy but useable state. No electrical bought, I rebuilt the MLPS and checked it, and installed the transgo kit. Trans broke apart from motor underneath car, using a 6 ft. 4X4 and some 2X4 to imitate Ford's 3 point engine support for about $35. I have no place to put a hoist or cherry picker. In fact entire deal done without a garage either, on a dirt carport floor, you don't wanna know how.... Next to God cleanliness required for ATX was one of the hardest things to attain.