There are ways to get 5 clutches in the forward and direct drums without machining anything...they came that way on the V-8 engine transmissions from the factory. All you need are the pistons for a V-8 application. The pressure plates(thick plates on the top of the clutch stack in the drum) come in many thicknesses, also, so the clearance can be adjusted properly.
Also, the forward drum(drum with the shaft) usually has a wavey steel on top of the piston that is used to cushion the apply when you put it in gear. The wavey steel can be left out to get one more clutch in, but it makes the forward engagements quite harsh...ok if you're doing a racing set-up, not so much for a street car. The direct clutch pack(drum with the sprag/one-way clutch) should NEVER have a wavey steel.
However...if you do not have access to the short pistons,
you can have them machined down to add one more steel/clutch. Personally, I would go for the shorter factory pistons, since machining can create weak spots, depending on how much is cut off. I have never actually had a piston machined, since I have the factory stuff available. In your case, it might be a better plan to go with machining.
hth.
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Joel Adams
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