Hi dewar,
Welcome to the RWA forum and audiocircle.
The Jensen PIO caps are pretty large and in the case of your dual-mono Clari-T with built-in volume control.... they will be extremely difficult to fit (most likely not possible at all). A larger enclosure would be needed.
I'm happy to live on less power and without an enclosure just to get a feel for what the signature 30 might sound like, and will then look to save towards a signature 30 should funds allow.
The Clari-T is a different animal than the Sig 30. I need to be upfront here... Even the most highly modded Clari-T (even with the PIO caps installed) does not have the Sig 30 sound. They are different designs (different chips, different boards, different parts) that sound different.
I don't recommend you DIY mod your Clari-T... there is a lot of delicate soldering to the board (which uses many surface mount parts). It is very easy it make a mistake, and this would void your warranty and could be expensive to repair (parts, labor, shipping, etc.).
For extra warmth, I think trying a tube preamp or a warmer sounding source is the better way to go.

Best regards,
Vinnie