Well.... lots of variables there regarding recommended grinds. The cam is the brain of the engine, and tells it where and how to produce power. Assuming stock engine and carbs, I don't think you would want to go much more than the "B" cam with SUs for a street car. Higher duration and a little more lift will give you a bit more power with a slight loss of low end torque, typically comes on at about 3200 rpms or so, a little later than the A. What rear end gearing are you running? Do you like to rev an engine or more used to torque? Honestly, I've haven't ridden in an A or B cam SU car much, so others should chime in who have. Also, the final drive gearing may make some difference in what the car feels like with A or B cam. Deans site has lift and duration info on his regrinds. You will also need to regrind or replace your rockers.
Dave Rebello grinds one, a happy medium between A and B. Stock A has a 256 Duration and B @280. His street is a 270 with a tad more lift than B Cam but complements the SUs. You want to capture as much cylinder pressure so I wouldn’t go crazy for street and drivability. Put in a 1600 rear end too and thin the SU throttles shafts. With longer dura cams you will have a bigger hole to climb out of.
Here's my old A cam dyno. SU's a little rough with an unknown needle. No point revving it past 5k but great for normal driving. Something slightly hotter and a nice tune with an Air/Fuel meter sounds like a good combo with SU's to me. Of course with the right needle and oil weight I heard they used SU's in the D-class racing making good power.
On thinning SU throttle shafts. When I flow bench tested SU carbs that I modified I found that totally removing the throttle shaft and plate did not improve flow. After I did a bunch of other stuff then working the throttle shaft helped. If the only thing you are doing is thinning the throttle shaft then don't bother. Why is this? Quick answer, take your calipers and measure the inlet and outlet diameters.
Personally, I think the B cam is a terrific all-around street cam. We grind a lot of C cams, but mostly because people ask for them.
The B is certainly smoother at idle than the C which has a noticeable lope. Whichever you prefer, there is only a moderate power difference between the two. We seldom use A cams anymore since there is really no downside to a B. C is a great street cam too if you prefer the lope.
Either will work well for you!
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If you want a B cam profile cut on your current A, one source is Delta Cam in Tacoma, WA. They have several grinds and are set up to regrind your rockers if they are the two piece. Otherwise, Dean at Datsunparts.com has everything you need and is now accepting one piece rockers as cores as he's figured out how to regrind and rechrome the one piece (well done Dean, more options!).