So long as you stick to the correct x flow or valencia type the head from the 1600 will fit, and likely have the biggest valves, if valencia use the stuff for a MK1 xr2 cam, head, personally I'd go for a single 45 rather than twin 40's, try and get hold of a Dellorto DHLA 45, these are much better than the DCOE weber and stay in tune far longer, they look very similar as designed by the same person, who now lives in Hingham, Norfolk.
A major problem with both x flow and valencia is rocker wear, if you have the money go for roller rockers, but as a bodge that works the rocker shaft can be taken out, turned upside down then spun 180 degrees so that it puts the unworn surface down most as this is where the wear takes place mostly, a ported head works really really well on these engines, just watch compression as some are combustion chamber in head, some are in piston.
tabetha