on a normal flatbed scanner for scanning positives, forget it. you wont get the resolution you need. you definitely want a negative scanner. the difference between flatbeds and negative scanners is that flatbeds typically only go to about 600 dpi, and some only 300 dpi. a decent negative scanner will scan at 1800 dpi or more.
i have a negative scanner, but the problem i'd have with your 8mm is that mine only is set up for 35mm and slides. you could do a masking to make the 8mm work, i suppose, but i'm guessing there are better negative scanners than mine, since i bought a fairly low end model.
ok, i just went to the site the handles my type scanner and there are much better scanners than what i have. some of these are scanning at 3600 dpi and can do 35mm, filmstrips and slides. i didnt see any mention of 8mm, but i would guess you could mask these and have it work. the site is:
http://www.scanace.com/en/
my unit is the low end 1800u/i and cost me $129 at staples and i've been quite pleased with it. do bear in mind that if you're using a windows based system you wont be able to use this with another scanner type device hooked up to the same machine....it's a windows bug. so, i simply put my negative scanner on a separate machine.
i'd also not go with the camera taking pictures off an 8mm projection. you most likely wont like the results.
if you'd like a test of a negative scanner on your film and you have a very small portion of the film you could send me without ruining the overall, i'd be happy to give it a test and send you the results or post it here.
whatever you do, hang on to that film and take very good care of it! Elvis memorabilia is a fairly hot item i would think.
Craig