requesting real life experience with 904 lock-up with manual switch

The A999 (32RH) is a hydraulically-activated (thus the H in 32RH) lockup convertor. No switch needed to function. However, a "Tow/Haul" switch was used in the truck versions to lock out the lockup ability when pulling loads.
Pretty much a bolt in for '67 and later A bodies, but the restrictive tunnel in early As requires a bunch of grinding on the 32RH "reinforcement" ribs on the tailshaft (not present on regular 904s) for clearance of the crossmember.
The 999/32RH also was bumped up to 3/8' cooler lines from the 904's 5/16".
Overall length and output spline is the same as a standard 904.