yes petcock on left.
If the harness, which is fairly slim, is attached to the frame rail there would be virtually no additional problem actuating the petcock. The 3/4" drop tube helps access but hurts the range of "reserve". A group did a study of various petcocks for flow rate. Getting a good one that flows enough is quite important. Low flow will lean out the carb on a high speed highway blast and potentially lean seize the engine.
There are few good choices for single off/on/reserve petcocks especially with BSP threads.
Map cycle # MAP0654 works and flows very good though I chased the 1/4NPT threads with a 1/4 BSPP die.Made in the USA dapco dexter mi viton seal not nitrile or buna so E-10 is ok
A custom thickness washer is needed to rotate the lever outward for access. Install without a locknut as you will loose reserve fuel but the thread start angle/phase will be random so each tank will be different/custom thickness.
Luckily my fiberglass dunstall ATLAS has dual outlets, unfortunately it is fiberglass
. So I will have to make a repop.