Really big, really powerful piston engines have issues. Sometimes, these issues are resolved.
A variant of the B-17 with Allison engine was made, but not really tested properly, nor was the B-29 with double-Allison. Other factors were at play.
A variant of the Hawker Tempest replaced the mighty 24 cyl Sabre engine with an 18 cyl 2-row Bristol Centaurus, then refined into Hawker Fury.
The post-war Wright and Bristol engines found a use powering airliners. How about the Allisons and Napiers?
BTW, the post-war Merlins which powered North Stars and Avro Tudors were specifically modified commercial engines, not war surplus.