Coldplugs, you're going to confuse him.. there is no twin weber setup commonly available for the stock MG head (and it would be way too much carb even if there were). I imagine he's talking twin SUs or a DGV, with maybe a DCOE or DGS in the back of his head... the link above pretty much outlines ALL of the readily available choices, but here it is in a nutshell (and I've actually dealt owned and driven (daily) cars with weber dgv, dcoe, SUs and ZS)...
SU - probably best all-rounder. Cool looks, good performance, decent reliability and economy.
DGV - can't be beat for economy or reliability. While not a performance carb by any stretch (despite what the catalogs tell ya) it'll still easily trounce a ZS-equipped MGB.
DCOE - the most versatile, flexible carb out there. If you love to tinker and know what you're doing. Mere mortals may not want to tackle the learning curve. Still, rock solid if they're set up right, and CAN be anything from a fuel-miser to a full-race carb.
DGS - May provide the best compromise between DGV and DCOE, but I haven't played with one myself.
ZS - not impressive on Triumphs, Jags or Volvos, an utter nightmare on a B, with that rotten manifold.