Noise: I protoyped a rangemaster (OK, sue me) with carbon resistors and an NTE158 Germanium transistor.  It did actually sound OK, but it was very noisy.  Reducing the collector resistor reduced noise, strangely enough.  For the production version I used metal film resistors, and this did reduce noise.  Swapping to a different NTE158 also reduced noise.  Finally I used a different part number transistor which had more treble and less noise.  There was a big difference in noise between the first and final version, so start with a selection of Ge transistors, use a transistor socket, find the best sounding one, and tweak the resistors according to R.G. Keen's article.

I did some final tweaking by ear using a transistor amp to get just the right amount of clipping.

Mix and Match: The Rangemaster does not have a high input impedance, so you can get more treble by placing a high impedence buffer circuit before it.  Place an average Ibanez / Boss / DOD pedal with it's effect "off" beteewn the guitar and Rangemaster to demonstrate this.  A Fuzzface in front of the Rangemaster give a variety of fuzztone/octave effects, a Fuzzface and Rangemaster in the same box with two stomp switches would be fun.  You could sell such a pedal (Dallas FuzzMaster). 

Keep it clean: The Rangemaster makes an vacuum tube preamp grid distort like crazy when you turn up the "Boost".  Using a clean transistor amp you can get mild distortion on the high notes, depending on the input biasing resistors.  You may prefer to adjust the resistor values by ear to get no clipping, and rely on a tube amp for distortion.  I would guess that the Rangemaster wasn't meant to clip at all, since it was sold as a treble booster.  Rory Gallager (interview with Vivian Campbell) said of his old Vox AC30: "It wouldn't be bright enough; therefore I used the Rangemaster", and Brian May (on the "Hot Licks" video) said he used a one transistor treble booster to cut the low end.

   GEO Rangemaster: "Austin Treble Blaster"