Switchin mains and half power

[paisley_tele]

I bought this power trans listed below it say it will do 270 or 340
I wanna switch inbetween them like some other guys he do. Its for a rocket so would 340 be to much. I got some 6n14ep tube too run. So whats u thoughts and how big of a switch to do tjis mod and the half power mod.

https://taweber.powweb.com/store/025130sch.jpg
[img1201]https://taweber.powweb.com/store/025130sch.jpg[/img]