Well, it's a puzzle for sure. I can't help thinking that the last thing you did was seals on the IP, and somehow that's important.

Um, you didn't disconnect the electric plug on the rear of the IP, the one that powers the idle speed positioner, did you? If that's disconnected, you're stuck with the low mechanical idle, 500rpm or lower, depending on where it is set. If so, it may not advance the fuel rack enough to start!

Good Luck
Jim