Is 270 close enough to 300?

I have two light weight lenses in Compur dial-set shutters from a long time ago:

1) 270mm Symmar Doppel f/6.8 that covers about 80 degrees based on the Dagor

2) 12" (304mm) f/7.7 dallon tele-anastigmat dallmeyer but not sure of the coverage (haven't used it yet)

The Symmar covers 5x7 but the Dallmeyer certainly does not so it will have to go! (since I am abandoning formats smallerv than 5x7)