The HD8 and HS8 are the most common 2 inch bore SU's, and at that, they are not too common compared to others. They were expensive to produce, and were different (especially the HD series) from the more standard HS6 and HS4 which made up most of SU's production in the sixties. Rover used twin HD8 and twin HS8 on their 2 litre four cylinder, and they ran just fine.
I installed a pair of HD8's on stock bore B20 with 10:1 CR, K cam, and ported head, and it flew. Made more power than the HS6's for sure.
I installed a pair of HD8's on a Datsun 260Z and it woke up screaming.
Not that I work on motorcycles, but when the piston is raised by the throttle linkage, and no throttle plate is used, that type of carb is referred to as a "slide valve" and operates differently than a "constant depression" type like the SU or Stromberg. Old English lawnmowers used a teeny carb much like a motorcycle. Lots of them around here too.
I know a few people with E-types. The quickest (although hampered by an agricultural gearbox) were always the Series 1 three carb 3.8 litre cars, at least according to the Jag zealots. I wouldn't own one myself.
The best manifold is still the integrated iron one without the secondary throttle plates. There is lots of room to port the flange out, and the heat at idle keeps it running smoothly.
SU talk is :
8 = 2 inch
6 = 1 3/4
4 = 1 1/2
2 = 1 1/4
1 = 1
with a few more variations thrown in.