question on a833

got car up a foot or so on all fours - was able to top up the fluid using a pump I use for outboard gear case that fits on standard quart bottles. Used some 80-90 Brad Penn GL-4 that claims safety for soft metals but I see is lighter than 120 service manual mentions, but a lot people here seem to feel is adequate. Took a half quart. Small leak from reverse light switch so planning to get a new one and suppose I will have to drain the transmission to install switch. Anyone know correct part? -it is a rebuilt 18 spline Hemi A833 4 speed but not sure if it is '68 like engine ..thanks