I've never done this in a 606 but I don't understand why the IP has to come off. Is this only to provide enough slack in the chain to remove the timer? After removing the tensioner, I'd roll the cam CW slowly stopping at the slightest resistance, which could be a valve coming in touch with a piston, to see if enough slack builds between the cam and chain to slip off the timer with the IP in place. This isn't just conjecture, it's Sixto conjecture. Attempt at your own PERIL!

Sixto
87 300D