The factory actually made an A13 with a 76mm bore and a 70mm stroke, but this would have been on the shorter 1200 height block. I think that this is what Feral has in his shed from some sort of open wheeler racecar. I think that many racers used them with good results in this class of racing.
Maybee Feral could let us know more. Details and pictures can be found
hereAt first oversize of 76.5mm bore you get about 1286cc but at second oversixe of 77mm you go over the limit with about 1304cc. I think that this would work out more cheaply and easily than finding long rods for a tall block. I hear that A12 blocks will bore that far, and the big bore A13 seems to be a bit hard to find, so an A12A with an original bore size of 75mm might be a proposition as I hear that the rods have the right pin size for the 76+mm pistons.