Fitted within 10 minutes, only had a few tight screws to get past and that was it, covers off, old valves out, lined the new valves up(which took a few attempts which bent a few of the connectors a little but just bent them back) then tightened everything back together again.
It really was easy so anyone thinking about it who isn't sure just go for it!
I'll find out more tomorrow when I test it at my band practice at higher volumes but at home I can actually have 12oclock on the gain without it being really dirty! But 3oclock is when it starts getting filthy.
I didn't even use the guide.......ok I just remembered it without looking thanks!