a few things... (been doing research for the same thing myself)...
schroth harnesses are very nice... forget the web address at the moment... they're street legal (most aren't), and they make a 4-point harness (about all you can do with stock seats anyway cause a crotch strap going in front of the seat doesn't do all that much) with a pushbutton release and single latch. i'll second Chumpy... according to my dad (ex-offroader), racing harnesses are a real pain to put on... i believe it. on to the next thing:
yes, racing harnesses have a definite 'cool' factor, which i understand completely, and i'll probably put them in too. BUT... what you're thinking of doing (as i understand it) just plain isn't smart.
1) racing harnesses, unlike shoulder straps, don't let you duck out of them if your car rolls. so, with no rollbar, if your roof caves in, you break your neck. which is why no rallying groups let members run with harness and no rollbar. so... put in a rollbar with harnesses.
2) you cannot use the stock shoulder strap mounting point, 'cause it's off-center. also, mounting them to the floor is one of the biggest no-nos (think about a crash... your body moves forward with pretty impressive kinetic energy, and unless the seat back holds -not at all a given with stock seats- your spine gets crushed). so unless you have a rollbar, again, it's not worth it.
good harnesses run about $150 apiece. you can get bargains looking around, just don't get the weapon-4 ones they sell on ebay (POS ricey knockoffs). and yes, wider belts are more comfortable.
nice-looking, comfortable seats are easy to get if you want to spend the $. try looking on e-bay for recaros, you can get decent deals (i did at least), and most are plain black or gray, cloth-covered, and adjustable, and metal-framed, unlike comparably priced seats from Summit (molded fiberglass with optional vinyl covering).
all of this is very extreme, i know, but you're installing seat belts so you'll be safe if a crash happens, and it doesn't make sense to leave out any possibilities. good luck, keep researching, tell me what i got wrong, i'll step off the soapbox now.
[ January 03, 2003: Message edited by: steppenwolf ]</p>