If you pull the trigger I've got Whitworth wrenches from my Brit days (when the BSA, MG and Triumph (car) dealers were going concerns) .... at this point in my life I need to admit I'm probably not gonna ever use 'em again (and be thankful).
If you're saying "what ... ?", this probably isn't the project for you.
Any advise on what to offer ....
IMHO it is worth exactly what you want to give on a purely emotional basis.
Seriously, you can't look at a project like this on the basis of economic or time-value analysis ..... bona-fide restoration will require quantities of both money and time that will have no relationship to the market value of the completed project for this rather un-remarkable (in the eyes of most potential buyers) BSA model.