I think you need to consider tearing down the motor. Get a list of everything that was done and rebuild it with a different goal than the previous builder. There's just way to much to consider if your gunna go with Nos. First question I have is are you going wet or dry? I'm assuming wet from your statement of being able to use the bottle routinely. But tear it down. See what's been done to the bottom end, is it 4 bolt?, has it been machined to 4 bolt?, has the stock studs been upgraded?, does it have studs?, the list goes on. But basically take the approach of start at the crank and work your way up if your goal is to use the bottle. If your not prepared to do that id just forget it and run with what you got.