Picking up on points made by others - we used to make some light-duty quarter turn drives using off-the-shelf Fenner 'Bi-loc' pullies which are grooved to suit both A and B section belts. So you can use an A-section belt while benefitting from the extended vee-sides as a lead-in.
We machined and filed a radius onto both sides of the vee-groove, so the belt didn't wear on a sharp corner as it ran off, or onto, the pulley.
We used a round-section polyurethane cord (about 8mm or 10mm diameter, mustn't bottom on the pulley though) as a belt, or sometimes an 'A' section Fenner Power-twist, or NU-T-Link belt (these are the Brammer (?) type link belts). It is important that the belts don't touch where they cross, especially the polycord which will quickly overheat. The only reason we used poly cord and link-belts was because we had fixed centres, otherwise I would avoid them like the plague.
BTW, after playing with these things for a few years, I hate them all! Especially poly cord drives. Yes they worked...but they were not trouble-free. We always had spare belts on the shaft. Our centres were pretty tight, maybe 250mm using 80-100mm diameter pullies.
Having said that, we had a 'Hayter' mower (still have it actually) which was exactly as Franco described, and never had any trouble with the standard (B?) v-belt and deep groove pulleys', I think the centre distance was quite large (at least two feet) and the pullies probably 4" and 5". I think the decent centre distance must help, plus a ordinary, strong, un-notched vee-belt.