Trutemper, the problem with drilling out jets, especially on propane, where you don't have a meter that you can clock, is getting the correct firing rate. (overfired)
All gas burners can be fudged, sorta, but maybe at some expense of reliability, safety, and ignition reliability.
What I mean by that is, you can drill the jets (too big) and fudge "some" by dropping the manifold pressure, or vice versa, but---
there reaches a point where the damn thing just doesn't work right, such as noisy, blowing flames, etc.
Pilot systems, especially, can be fussy, because incorrect ignition (due to poor adjustment) of the main burner can blow out the pilot.
Also, because your drill bit "roughs" up the inside of the jets in an uneven manner, there is no guarantee that a carefully drilled/reamed jet will flow the same as it's brothers, thus overheating and warping or cracking various sections of the heat exchanger cells.
In addition, as I mentioned, without a meter, how do you know when the unit is overfired? With a normal propane burner, you assume this by setting the required manifold pressure, and insuring the correct (factory) jets are in place. On a ducted system, you can double check by measuring the temperature rise, something that is not really possible on a unit heater.
(I guess you can assume that if it doesn't cycle on the high limit, it's "ok")
It's been a number of years already since I've serviced atmospheric gas burners, and even now, I'd be reluctant to judge a burner as over/ under or correctly fired just by visually inspecting the flame size.
This is fairly thin ice, and is pretty much forbidden by most any codes, or just plain servicemen's common sense.