Did some Montesas 2ts come with a curved inner muffler tube, the perforated one that gets fiberglass wrapped around it?  Are they still available somewhere?   What years and models came with them?  Did they make the bike quieter than a straight pipe?  I have an 01 Beta I would like quieter and wonder if this is an option.      

Have you repacked your own exhaust, including the centre box? 

If you want to try doing it, should be easy to get a piece of alloy tubing on ebay and drill holes in it yourself.

I bought the right size perforated steel tube for my 348 in the form of a go-kart muffler core and it was very economical. I didn't need to curve it though

This bike was a rare find and is just starting to show wear on the original tires.  I inspected the exhaust and it is very clean.  The 270 has a reputation of being on the loud side.  The root of the problem is that I have been spoiled by the sound level of a Beta 4t so am looking for any options to quiet down the 2t.  I put an FMF universal muffler on a TY175 and liked the result but it looks too wide for the Beta.

I do remember hearing of people replacing the curved Montesa inner pipe with a straight one for improved power and "better" sound.

      

Straight through tube gives bike a little bit more zip. Just as quiet if packed correctly.  Got my last one off Mark at H&D, very reasonably priced.  Cheap hop up mod.  Mitani do a longer version of pipe, along with epic price tag. Meant to be a Fuji works mod or something like that.