That article covers the basics pretty well, and I only saw maybe a dozen little details they forgot to mention. The 400 is diferent, not necessarily more difficult than the 350. There are a couple of snap rings around the center support that can be swapped, one with square-cut sides, and the other with a taper on one side, and if they're installed wrong, the trans will shift to 2nd. gear once, and pop the ring out of the groove in the case, requiring a complete teardown again. (Don't ask me how I learned that one!) If you don't de-burr the manual valve shaft with a file before removing it from the case to swap the seal, you'll score the case and end up with a leak that can't be fixed. Machining on clutch pistons is an advanced-level technique that should only be attempted by a real pro. There are lots of clearance issues to deal with. I'd suggest finding a mentor who is very familiar with transmission repair to guide you through your first 20 or so rebuilds, before you attempt it on your own!
Jerry
