My current SL350K0 as purchased. Not running.
Coupla weeks ago. Motor has been bored out to 362cc, has high compression pistons, 34mm Mikunis, 1-1/2" exhaust into Supertrapps.
Also, the head has been ported, back-cut valves, Megacycle TT grind cam, electronic ignition, Dyna coils.
Motor makes pretty good power now.
Currently have the final drive ratio at 2.53:1. CB350 was 2.25:1, and later SL350s were 2.625:1.
I consider this bike an excellent back roads prowler. She can handle gravel and dirt roads just fine, and has plenty of power in 2nd, 3rd, and 4th gears while navigating hilly, twisty roads.
With the current gearing, she will easily pick up the front wheel in 1st, but not in 2nd. 50mph is 5500rpm in 5th, and it's relatively light, so it's not a comfy highway cruiser. Off-road, she doesn't have the power-to-weight ratio and suspension of a modern thumper, but she can still get you there:
As for parts; many are interchangeble with the ubiquitous CB350s. There are a lot of used, NOS, and aftermarket replacement and speed parts still available. Mufflers and NOS steering dampers command a premium, and good tanks, side covers, and fenders will continue to become more rare, as they are specific to each SL model change. i.e., a K1 tank will not fit on a K0, etc.