Quickest SOHC I personally witnessed was a carbed gas turbo 970cc. It ran a 9.10 at 142 in Sacramento.
I'm know there were plenty of quick ones out there but don't remember what they ran.
We won't count the Nitro bikes here.
Eraldo Ferracci (yeah, that desmo guy) ran a SOHC turbo.
I have some very old phone notes from him here:
8.60's @ 168 mph. on 6 1/2" road race tire.
1020cc, 72 bore X 63 stroke. 9:1 Arias pistons. Stainless Steel top ring.
F-2 cam.
Bike ran 8-12 mph faster with aluminum rods vs steel (with no other changes), his opinion was because of their elasticity.
28 psi boost, 32 ign lead.
Head? If he said I didn't write it down.
5 speed w/ air shifter, GL 1000 clutch, shift at 9,000 rpm.