a bit of research...these are the original part numbers FROM THE SERVICE MANUALS  which I cross checked with the PRB line

http://www.russellind.com/prbline/xref/jvc.htm

If you can't get them (links below) & still want help I'll be glad to help, don't worry
M90
VKB3001-012 Capstan Belt SCX7.0 (square cut, .040-.049 inch/1mm thick, inner circumference 7inches)

http://www.partstore.com/Part/.../VKB3000012/New.aspx
VKB3000-017H Take up belt SCX4.6 (square cut 1mm thick, inner circumference 4.6 inches)

http://www.partstore.com/Part/...VKB3000017H/New.aspx

VKB3000-031H Counter belt SCY5.2 (square cut .035-.039 inch thick or 0.8mm inner circumference 5.2inches)

No longer available??...don't worry  ;-)
http://www.mcmelectronics.com/...Y-MCM-SCY5-2-/SCY5.2

M70

9731201CT Main belt FRM9.6 (Flat belt/medium) inner circumference 9.6 inches
8001602T Counter belt SCY7.0 (square cut .035 X0.035) inner circumference 7 inches

very informative man, thanks

i dont need them right now but is good to know.

I'll second Chris's coments. A sticky post for tech specs would help immensely as well IMHO, as would links to international suppliers. I'm finding it very difficult to get parts for cassette decks and walkmans

Thanks DocP for the research! 

Boomboxery.com has a topic intended for that. Guess we could start one out here too. Usually data gathering is a frantic exercise performed only when you need something...we most ofetn forget the details once we've gotten things fixed...so it becomes difficult to 'share' exact later after some time has passed.

There is of course a more 'sinister' reasoning....if everyone were to know where to source the right parts and belts there won't be many steal deal 'As is'/'Not working' listings  for us to grab and enjoy ;-)

Thanks for the info DocP.