I've run basically both of the above systems on an A500 in a '71 D100 with a mild 318 (PATC wiring diagram), and an A518 in my wife's '79 LRE with a 9.5:1 360 (delay timer). In both cases, I used adjustable pressure and vacuum switches to fine tune the system and didn't use a toggle switch at all. Running a vacuum and a pressure gauge into the cab and having someone drive it so you can record actual readings to get a starting point for settings helps, but it takes dialing in to take account of vacuum changes when OD and LU kick in. Both ran flawlessly for 10+ years before they were sold. Remember that 1 lb line pressure = 1 mph IN THE ORIGINAL VEHICLE. If the donor vehicle had a 3.08 gear and you're putting it in a truck with a 4.10, a 50 psi switch WILL NOT engage at 50 mph (that's why I used adjustable switches).

In a truck, mounting the OD trans is as simple as fabricating a new rear mount and shortening the driveshaft. On the LRE I picked up a slight vibration at certain speeds because I didn't match the u-joint angle when I did the new mount, (u-joints at the ends of a shaft should have similar angles) but an angled shim on the rear spring mounts solved it.