Original muffler are not problem since dieselengine are powerful, but you must lead the exhaust away from fuselage cause much oil (20-30% oil) in fuel.

Select bigger propeller until 30% than normal propeller, then fuel consumption will be 50% less than glowengine.

If engine run fine with original carburator, do not need to replace smaller carb.

You can use tachometer, but i self never used tachometer to checking rpm. Imortant there are not hard sound (knocking sound) cause to high compression, back off compression until hard sound are removed and the engine are running fast without rough rpm.

Jens Eirik