Lumpy cams have "less driveability" because they make less HP than the stock cam at low rpms ... and with the corresponding big valves, intake and exhaust, you lose power at low rpms. Tall tires on the back make this even worse. However if done right, it's all outweighed by more HP at high rpms.

One thing to do is get a bigger engine (A14/A15) with a lumpy cam, so you still have as much HP as the A12 even at low rpms.

Datsa73's engine sounded real good (in the photo album). It is A15 with lumpy cam, dual downdraft webers and maybe 2" exhaust with a "glass pack" (straight through) muffler. A little loud, but sounded good at all rpms. It "howls" at 7-8000 rpm. At idle it sounds a little like the choke is stuck on, but muscular sounding.