The ideal head to start with is the injection head, std ports are slightly better, so less modding needed, when going for a 2.1 the CR will be raised anyway.
If you are thinking of side draughts, 40's will be too small really you need 45's with 36mm chokes, ideally dellorto DHLA45, a much better carb than the weber DCOE, but forget economy or driveability, will kill low down response due to air speed being so slow through the carb, all depends on what power you want, but if only 130/140 I'd forget the twins.
tabetha