The 67+ 904 rebuild kits are easier to find. I recall ~$80 on ebay. Those are the "banner kit" (without steels), or ~$100 for a "full kit". Don't get the "overhaul kit" since just rubber and gaskets. More expensive kits (>$200) have upgraded clutch plates (Hi Energy, Blue Plate, etc), but don't know that matters unless you are racing. I rebuilt a 413 tranny last winter, which is essentially the same inside. The engine had been flaring from 2 to 3. Several clutch plates were worn to the metal and their inner teeth almost gone. It was a prior rebuilt tranny I bought used, with a "Certified Transmissions" sticker.
They had cheated and re-used worn clutch plates by adding an extra steel plate. That is why better to do it yourself. I would allow a week or two. I found worn output bearings I had to replace. I rebuilt 2 Mopar trannys this year and the steel plates were all worn <2 mils, so I re-used. Optimal if you have a spare tranny in case you find worn "hard parts", which can be very expensive.
