Thanks for posting this, just got one myself and the picture of the drawing confirmed mine is right. I just had to reseal the hot tube. My burner is also dirty but the looks of it as the flame is yellow.
the glowplug wasnt really a bad idea, but the CHOICE of glowplug was... standard nitro plug, its platinum, (or at least platinum plated these days) very fine, no thermal mass, and its really only meant to work with methanol. a catalytic reaction, not just the heat that makes them work. and at the speed this runs... that thermal mass is the big issue... especially when its "missing" and blowing nice cold air over it... even at full speed its still below the idle of a glow engine and they dont really like idling much because of the plug? the old plugs even have "idle bars" welded across in front of the element to try and address the issue... try using a 12v heater element. bit of hunting online, you can find ones that are far more suitable... ceramic, plenty of surface area and thermal mass... im thinking the igniter from the diesel heaters would be about perfect... a diesel engine glowplug would be all out of scale... either way, there is a massive selection to choose from. ive actually been playing with the idea of making a "hot tube" using one with PWM to address the issue of "thermal runaway" when you start pushing the power up... would like to see a standard B&S running on diesel, say... just for giggles... i hope if you do make a new shaft that you resort to proper shrink fits rather than amateurish methods such as silver solder or, yuk... all offense intended... loctite! as it is, youre just repairing it so dealing with what you got... loctites acceptable.. but only just! i feel the pain... nothing worse than turning a recalcitrant engine over... at least it doesnt pop. mere pops are even more painful than nothing at all...