" A friend of mine is wishing to replace his worn out carb with a new Mk1 concentric, this is on a 350 Sebring. As far as I know its standard apart from a green/white cam. "
____ This seems interesting, wish you told us more about that Sebring -(n-c.350).
I'm left to assume that the stock 24mm-Dellorto is the worn-out carb being replaced, and the cyl.head (other than cam) is still stock. (?)
__ It's so typical that some dude who wants to race his Duke has been led to believe that it needs a Green&White-camshaft... (Which indeed is fairly useful for CONSTANT high-RPM racing, but also a certain handy-cap for running on tracks which make good use of 1st.gear !)
I've never tried-out running a G&W.cam within a stock Sebring-head, but still I'm very sure that the outcome would be fairly poor ! ...
First, the low-end power (which a stock-Sebring has in spades!), would be drastically reduced, (yet still better than that of a stock w-c.350),, and second, the top-end power, (which is where the G&W is supposed to excel), can't be too greatly increased (over stock) because of the Sebring's small 26.5mm intake-port and small-sized valves.
However the change in mid-range power-delivery could be interesting,
yet I'd bet that on a 'FUN' race-course, (which makes good use of 1st.gear), a stock-Sebring (with the Violet-cam), would still have the overall-edge/race-advantage over a Sebring with a G&W.cam.
____ Please let us know if any port-work (or anything) has been done to the stock cyl.head/(top-end).
" Does anyone have the jetting for one of these that can be used as a starting point? "
____ Sorry that I-myself don't have those specs for you but,, assuming that the D.350 will be running without a 'muffler', then slightly richer than the jetting-specs of a 1974/75 Triumph 750-twin should be very close to what you'd end-up with optimally.
__ You didn't mention the size of the intended Amal-carb,, but anyhow, in most any case, the jetting listed within this-other post -
viewtopic.php?f=3&t=1160sid=32cb4e913d90d796c8c06ac6fb13d81a#p8046 - ought to provide a close starting-point for you to follow & possibly start-off with.
Hopeful-Cheers,
-Bob