NO TAPE! The 555 is a paste. If you can't find the 555, I think it's called Uni-lyte or something similar to that. It's actually used for sealing threads on black iron natural gas lines. And yes, it will throw off your torque specs. But look at it this way. Right now your torque specs are dead-ballz on..........along with leaks. If they say to torque to 85 ft/lbs (By the way, what's with all the car shows saying "Pound Feet" of torque now? When did "they" change it, and just for the record I'm not switching. It's "Foot Pounds"
) I add a few just for that reason. If they say 85, use the 555 and torque to 87-90. Not saying the 555 WILL fix your problem, like I said my buddy tried everything under the sun, and the only thing he found to work was high-temp silly putty. I shudder at the thought, but ya gotta do what ya gotta do.
If the head bolts are leaking coolant into the cylinders, even minute amounts it'll have trouble starting when hot (cuz the cooling system is pressurized) once it cools off (no pressure cuz of the leak) it'll fire right up. I've heard of crazier things happening!
Try the 555 first, then other options are Indian head, Permatex makes a non-hardening sealer in a tube, and then there's the high temp ultra grey as a last resort. The other thing I'd do is drain the coolant, torque down the bolts with the new sealer, then let is sit for an hour or so. Let that stuff set up, THEN refill the cooling system.
Keep me posted on this one bro.