I've never installed alarms, but it seems that if you installed the starter interrupt on the purple wire in the cab, it may be relatively easy to find and defeat after a break-in to the cab. If you installed it in the engine compartment/starter area it would also be fairly easy to find, but the thief would have to open the hood and be crawling around in the engine compartment. That's probably more work and less likely to happen. Also, did it come with the starter shut-off relay to install in the wire?
Did the Viper come with instructions for how to wire it with different power lock systems? It has positive and negative trigger outputs, and I think the exact operation of power locks is different between manufacturers. You just need to know which way the GM locks work.
The lighting output and some of the other outputs are listed as optional. On my keyless entry they can be used to flash the park lights, turn on/off interior lights, and perform other functions, but my system is very simple and I need additional relays to make those functions operate. I left them all disconnected and just used the output to the lock solenoids (which came with my system for a '75).
Bruce