SU every time, I took my Weber off and replaced it with SU again because it kept cutting out on big inclines, and again I can guarantee you they do run upside down.
mine was off of a Metro 1.3 cost me £10 from local scrappies, made adaptor my self which took me about an hour, fitted new choke cable off of a Montego, cut end off original throttle cable and fitted solderless nipple, and then the air box came off of an early Mini 1000
total job cost me less than £20 and about 2.5 hrs of my time, well worth it.
Just make sure you keep the adapter as short as possible as I have heard people have severe problems with the carbs freezing up, got to say that I have not had the problem on mine and I have run it for 2years now.