The original 2 power tube version only allowed for 2 6V6s anyway, of course you could beef up the transformers and make a more powerful version but that changes the original idea. As it is, the 2Stroke is on par with other single ended, cathode biased amps on the market.
Considering that the Weber kit comes with Alnico speakers and a cabinet, the price is pretty good. I would consider upgrading the Weber Alnico speakers from the “Signature” series to the “Classic” series. I tried both in the 2Stroke and although they both sounded fine, I liked the Classics better (they are more expensive though).