I have to agree with what Greg said re power and rpm.
Further to that , why do we swing bigger props? well as we all know diesel exhaust is cooler than a glow exhaust , why ? well diesels generally have completed combustion by the time the exhaust opens wereas a glow is still trying to burn the fuel so flame is emitted out the exhaust- dont beleive me , try running both at night with open exhausts.
Its the more complete combustion and the higher energy fuel that gives diesels both the better fuel ecconomy and the higher torque at low rpms, hence the ability to swing the bigger props better than a glow.
Now will the diesel conversion on a pipe go as well as on glow, it should but as Greg said it will require a similar sized prop to do so.
only benefits of running a diesel on pipe are better fuel ecconomy (we still have higher energy fuel) and the COOL factor to make the diesel nay sayers stand back
Stewart