I just delivered a 540 race engine to a customer. If you have the block I believe the 4.25 stroke X 4.500 is the way to do it. Although this was an early Mopar mega block , we went 4.375 bore with 4.5 stoke to preserve the block for future use in bigger bores. Fully ported TF 240 heads with a roller Made 850 on the pump. Full race deal. Testing at the track has been limited with all the virus crap but early signs are promising.