Sid,
How much power do you think it takes to drive the blades at 60% flat pitch.
A standard procedure on the old S-76 A with Allison C30's was to start and stop
with one engine in idle and the rotor brake ON.
Brake ON start an engine - brake OFF - start second one.
Shutdown one engine - Brake ON until blades stop - shutdown second one.
Even with 2 engines at idle the brake was man enough to stop the main rotor
as long as it stopped without a blade being over the exhaust.
I know the brake in a 135 isn't up to it but the drive train certainly would be.
At MIN FLOW I would guess that each each might make 30 HP at best.