273 and 318 the same block?

Nice idea but there is one fly in the ointment. Ma Mopar in her infinite wisdom used different water jacket cores in each block in her efforts to make each one as light as possible. The cylinder walls in each block does not have enough thickness to allow much more than .060" overbore. The one exception to this is the '71 360 blocks which were cast using 340 water jacket cores and can go out to 4.1" safely. Hope this helps...