i didn't even read the whole thread
Chassis dynos work on tractive effort and ramp-down inertial loads to come up with an a.t.w power figure- there are many things that the dyno operator can tweak to influence the final figure (ramp rate, correction variables, etc)
With sensible wheel sizes (16-19 inch, tops) with normal road tyres and normal pressures, and using a DynoDynamics rolling road dynamometer running in shootout mode only, I'd stand by a multiple of 1.30-1.40 giving a fairly accurate power range at the fly.
But what does it matter anyway? A Dyno is a tuning tool- may as well work out the power at the piston crown. It counts for s.f.a