I don’t think the slopes carbies were because of height issues ,The old WOBentleys had plenty of clearance under the bonnet.
The downdraft carbies… Prewar the SUs relied on the weight of the brass damper,and postwar, SU found that alloy dampers were cheaper to make but needed a spring to compensate for being lighter.
The downdraft didn’t have this gravitational assist.
The Rover Carbies shown have post war float bowl tops , the overflow tubes are a sensible mod, but one has to be careful about mix&matching as the mounting point for the two types are incompatible .
I have finally remember one of the examples where the rule about SU type numbers doesn’t match the size.
The HV8s are actually only 1 7/8"
Many years ago SU were owned by BMC who realised that production cars were moving to fuel injection and decided to sell off SU.
Included was a museum of all the old types they had made and H8s and parts there of.
The gentleman here in Sydney, knew all this and wanted the lot . So while the locals were hoping for some cheap cherry picked bargains , he made a killer bid for the lot, and got it.
There were protests that this historic collection should not be allowed to leave UK. But by the time they got round to making representations , it was on the boat and bound for Australia.
So H8 s were sold from parts in the stock and when parts ran out more were made out here.
And the range expanded to include the 2" to 2 1/2" carbies .
The maker here in Melbourne basically started because an ERA owner asked him to copy on of the big SUs used on the ERAs.
Which is sort of where this subject started.