Nik,
Would it be possible to get a version which would allow to switch from standard HRM to Bluesmaster HRM, all in the same amp ?

I think even thought the extra gain is fun, the stock Tweed circuit offers more than enough gain and is more versatile and musical in the long run.

That Champ Vibrochamp difference may not be cap, it may be extra resistance in the signal path introduce by the trem circuit.  In the larger Blackface Fenders, the "vibrato" circuit adds about 56K of resistance; obvious the VC uses a complete different circuit but I don't have a VC to poke around in. 

On mine, I have the cap switchable.

If you just do the mod you have posted, you are getting soemthing a little different just Tweed 5F1 tone.

Fender had to introduce more gain in the preamp of the BF Champs to compensate for the higher resistance of the BF tone stack.  Remove the tone stack and you end up with a ton of additional gain that Tweed Champs didn't have.  It creates a hot-rodded, fire-breathing monster of an amp. It's a fun little crunch machine, but much, much hotter than a real Tweed Champ, and sometimes it would be nice to dial it back to get some tweed cleans.

So, to balance it out, we switch out the 2uF electrolytic coming off V1B's cathode.  This creates a much more dead-on 5F1 sound out of the AA764 circuit. 

Is that the basic Gerald Weber Tweed mod?

If you are switching out the Tone stack, make sure to lift the 2uF cap off the pin 8 cathode, or have it be able to switch out.  otherwise you end up with a massive amount of extra gain  from the loss of the tone stack.

I was lucky enough to find my ots used.  Love it. There are a couple of things i'd like to mod and was hoping for some advise;

1) I would like to have both the fet and normal imput summed together when both are plugged into. When both are plugged in it defaults to the normal.  I have a 1942 archtop w/ both an acoustic polymer strip type pu and a mag pu hanging from the end of the fingerboard.. 

2) I would like to pad the output of the clean channel by 6db or more. The reason is I like to run the clean volume knob high- more warmth in the clean channel, while also having the od trimmer set pretty low- about 9o'clock and using only a moderate amount of gain in the od channel. When set like this the ratio knob cannot entirely make up enough gain to make the od channel louder than the clean channel.

any thoughts? much thanks

Here is a new one, hope you'll like it

My Les Paul works well with the non-HRM!