I'm not a fan of using tubes other than what an amp was designed for. People claim they add headroom by using lower gain tubes, but it's the same as turning the volume down. A lot of mythology about amps and tubes, etc.
There is a sticky thread above in the gear section all about Blues Jr Mods. hasn't had any new posts in a year, but there is some good stuff.
Blues Jr's were all the rage when I started BGU. Mostly because Griff had a video of himself playing one. Then it was the Mustang, and now it is the amp sim stuff and using a PA for the amp.
It's all good.