I worked at a GM dealer for a bit and got to drive a few trucks with that motor. There was a tech there that had stuffed one in a '70 Monte Carlo and he took me for a ride. Both the trucks I drove and the Monte had stock engines with auto transmissions.
All I can say is that Monte HAULED A**!!! The Monte was going to be set up for drag racing but still had stock suspension when I rode in it. It was actually kind of scary how poorly that car handled that motor.
The engine itself is a good unit. GM quit making it only because the 6.0 in the trucks was doing better in sales. The 8.1 got such poor MPG and the gas prices were going through the roof, it didn't help either. (the Monte had a stock truck computer and modified harness, not sure about the throttle)
That engine in a 69 vette would be pretty cool. The aluminum heads would help alot if you can get them. That is a huge, heavy motor but strong and reliable.
I can't tell you anything about the harness and computer running right from an LS1. I would try and get a comp from a truck and tweak it instead. They are cheap in the wrecking yards and can be programmed many different ways.
Good luck with the hood clearance.
Post some pics when you get it installed.
