I've heard "rubbing on it for weeks on end" makes you blind. But whatever...
As far as the paint is concerned, I guess it depends on what kind of finish you want to end up with. You can use paint stripper, I recommend "Aircraft Remover" brand, but it will probably discolor the metal. You can use some sort of bead or media blaster, it'll be messy if you're trying to do it with the engine in the bike. You could also try using localized heat and a wire brush....
well step 1 is to pull the motor out of the frame as is the norm with any work you have to do on a cb750 motor.
I guess the dumbest question is first: why do you want to remove the paint? and also is it from various components or the whole thing?
I can see removing it from the valve cover and even from the engine side covers but the main cases are hard to work and will usually require blasting to get all those hidden areas.
Honda used some pretty tough paint on the F2 engines (they are special cb750 motors if you haven't figured out yet) so the most at home way is to get a real "aircraft stripper" (like the brand aircraft stripper) and not one of the cheap-o brands like some bodyshops use. Some chemical stripers can dissolve aluminum, but the ones specifically forumlated to work on airplanes won't (because airplanes are mostly aluminum). I guess what Iam trying to say is make sure any chemicals you use (espically degreasers like oven cleaner and the like) are aluminum safe.
soda blasting would work BUT it ain't cheap. A lot of work to prep it, you would need to disassemble the engine entirely and remove all seals gaskets etc. then you need to find someone in your area who can do it. Worth looking into. Who knows there could be a shop set-up to do it nearby. Pricey but the results are second to none.
I am a painter by trade and have removed a lot of finishes. the aircraft stripper is gonna be your best bet like those guys already told you. there are a few other chemicals you can by at your local paint store that will remove paint and even epoxy's. MEK (Methyl Ethyl Ketone) for instance however you stand a good chance of removing skin, fingers, ect.. I use some nasty stuff and I won't hardly use it. as far as the aircraft stripper is concerned if it is cold out, your wasting your time. you need to be in a warm sunny place if that paint is as rough as they say. I tride stripping a '57 caddy and it would only take that old stuff off it it was out in the sun. talk to your local paint shop(sherwin williams, kwal, benjamin moore) some of those guys carry some wicked stuff in the back. you may just find idiots too. but if they know there stuff they should be able to hook you up!
mek will melt the gloves you use onto your hands if you arent careful. evil shit, creates synide gas when burned. i once stripped the entire finish off of a desk with a plastic putty knife and mek in a matter of minutes. the atf used it as a propellent for the tear gas they sprayed into the branch davidian compound just before it burned. tin foil hats asside.
I told you you would lose a couple fingers. You wanted to know how to get evil paint off, you use evil solvents. and yeah in the big leagues most of what we use will melt plastic scrapers... yeah if i ask the same question on hear you know why now. I play with this crap all day. I'm epoxy coating floors today!!! fun fun. but seriously there are solvents out there that will remove that paint. it's just up to you what you wanna use. the mek may destroy seals and gaskets too. there are some pretty wicked gun cleaners out there also. Kwal paint sells a product called liquid dynomite it is the best paint stripper I've used in houses, not sure how it would be for auto applications but it was faster than the aircraft at removing interior oil enamel. hope any of this helps... I may just be rambling