The trick is not how long the starter is engaged but rigging it so there is one signal to glow and another signal to crank. It can't be too complicated for the right sparky to device a 10 second delay. Worst case, you get a second remote start unit or use the accessory feature of a remote keyless entry unit to start the glow cycle.

As Brandon says, use any normally closed vacuum switching valve from a wrecking yard to effect shut-off. The vacuum circuit is tight between the key switch and the shut-off valve.

I've never heard that there's any difference between the starter or starting circuit of an 81 and and 83. Certainly not in any way that would make it easier or more difficult to add a remote start feature.

The typical advice around here is to search the archives. Don't forget to search the internet as well -

http://shop.store.yahoo.com/gigabuyz/aps55lra.html

http://www.crimestopper.com/remotestart03.html

Sixto
95 S420
87 300SDL