I just got done putting a 65cc Metrakit on an E-50 with just a Dellorto 16.16 SHA - 82 jet, 3-shoe clutch and it still has the Bi-turdo that was on the bike when I bought it. I also put a 50cc hi-comp head on it. Gearing is 16:45 (just put a bigger one on front for now). I match-ported the transfers and that was it. The guide on the Wiki is great.
After that upgrade without a lot of hassle, it's ripping at 48 and hasn't given a lick of trouble at all.
Nice thing about Metrakits is they are cast-iron cylinders, so if it should ever hard-seize you can get it bored out and upsize.