doing rebuild on 904 what needs upgrade?

Does "stock converter" mean the one in your 68? If so, you need a spacer ring for the snout of your converter to match the larger hole in the 360 crank (all ~71+? LA engines). Also make sure the 360 was for an auto since the crank hole might differ in manuals.

I always wondered if the racing type clutch plates buy much for a daily driver. They sure cost more. Do they give more life? A standard 67+ 904 rebuild kit is ~$90 w/ steels (ebay). I haven't done a 904 but rebuilt the similar A-413 torqueflite a year ago. I got the Mopar "Diagnositics and Repair ..." or such-named manual off ebay ~$10. I later found the ATSG manual on the web and found it a straight copy and even less info. Might be true for 904's. The manual is very easy to follow, with detailed drawings for each step. The trans looks fairly simple when taken apart and not many ways to put parts in wrong if you sign-off each step. Just get a set of snap-ring pliers w/ some big ones (Harbor Freight).

I think the servo piston upgrade is to fix a common cocking problem. I thought the upgraded one cost ~$25, at least it did for my A-413. Shop around.

A shift kit is a good idea, but I would stay with a street version. It gives quicker, firmer shifts, which will save your clutch plates wear and maybe improve mileage. I didn't notice any kick after doing so in my Newport's 727. I can feel the shifts and maybe I never did before the kit. The factory always designed slow, slippy shifts because that feels smoother and sells cars to the undeducated public who think smooth shifts are the sign of a good transmission. If you want to feel a kick, drive almost any 1980's Mercedes 300D, like mine. They slam into 2nd, usually due to problems in their quirky vacuum controlled shifting.