A word of advice when it comes to pre-heating... Wrap the engine cylinder, not the muffler or header. By stealing heat from the muffler, you're taking heat from the very place you need it the most.
How could it really matter? If you don't preheat, you'll be putting cold oil into the muffler, it you do wrap the header to preheat, you'll be putting warm oil into cooler exhaust gasses in the muffler. If you wrap the cylinder to preheat, you'll also be cooling the exhaust gasses. I guess I can see that there may be
some difference, but is it really that much, and why?
Phil