shovelhead big bore question

i have a 66 shovelhead, its setup for big bore jugs and heads. i think it was at 96 inches. i was wondering if anyone knows if i can go back to 74 inch jugs or 80inch jugs? im pretty sure the cases have been machined to fit the big bore jugs.

if it is not possible to go back to the stock size whats the smallest size big bore i can go with?
thanks