Maybe try a air -> water i/c and fill the water with ice. That should reduce intake temps quite a bit
Also just a thought - we are being too harsh the question is quite simple, so:
was wondering if i can fit a blow vavle to my stock TRX 91'.
Yes you can fit a BOV to your TRX, it can be installed anywhere within the engine bay (or cabin for that matter). I think a nice blob of bluetack should do the trick.
Unfortunately although the BOV will be installed on your '91 TRX it will not make any f00ly h3kt1c sounds, in fact it would do nothing, but it
would be "fitted".