Padding a tube FX pedal

[luthierwnc]

Hi all and thanks for looking.  I'm re-purposing a small rack unit along the lines of the attached schematic.  It's just a Deluxe Reverb clean channel as near as I can tell.  My plan was/is to use it as a preamp after the pedalboard going into a tube amp. 

Couple things:  one, the signal will be coming in fairly hot.  Should I make the 68k grid resistor a pot to pad the supply and two, those tone-stack cap values seem awfully generous.  Do you think .022's on the Bass and Middle points would be better considering the signal will have already gone through an assortment of pedals?
Thanks, sh