I do miss the days when the old 727s and 904s had convertor drain plugs and you could easily change 100% of the fluid- the irony being that those transmissions were so overbuilt that they rarely ever *needed* a fluid change...
Preach on Brother. Preach on!

WHY auto mfg's in general no longer have the TC drain plugs is beyond me?
I gather that when Chrysler was scrambling to get their first lockup TC design in place (remember this was circa 1976, one of those not so good eras for Chrysler financially) that the lockup clutch material was located right where the drain plug would have to pass through it. So the drain plug was deleted rather than coming up with a fundamentally different convertor housing, which would have had a lot of ripple-down changes.
Now why OTHER companies lost the drain plug, and why Chrysler didn't put it back in later years, like the early 90s when they were swimming in money, remains a mystery to me. Being a bit of a cynic, I think it has to do with making things appear to be "sealed for life" which appeals to a lot of buyers out there. Same as with Toyota and Chrysler removing dipsticks from their automatics now

As for 904 vs 727- have you ever opened both up? The 904 is for all intents and purposes just a scale-model of the 727. They even can swap valve bodies and a few other parts. The 904 has lighter gears and lighter/smaller clutch packs so its got significantly less parasitic power loss. In stock form, I wouldn't put it behind anything bigger than a 318, but with some modifications, it can handle a lot. The later "A998" and "A999" versions of the 904 had a deeper first gear ratio and extra clutch plates for truck and copcar use. For a while, drag racers liked to put built 904s behind big blocks and hemis (even though adaptors are required- no 904 was ever made with the big-block bolt pattern) because they lost less power in the transmission than with a 727. Of course they weren't going for longevity, either... I'll keep my 727s! :-)