Re civvy Merlins, from Wikipedia...
With the end of the war, work on improving Merlin power output was halted and the development effort was concentrated on civil derivatives of the Merlin.[22] Development of what became the "Transport Merlin" (TML)[23] commenced with the Merlin 102 (the first Merlin to complete the new civil type-test requirements) and was aimed at improving reliability and service overhaul periods for airline operators using airliner and transport aircraft such as the Avro Lancastrian, Avro York (Merlin 500-series), Avro Tudor II & IV (Merlin 621), Tudor IVB & V (Merlin 623), TCA Canadair North Star (Merlin 724) and BOAC Argonaut (Merlin 724-IC).[24] By 1951 the time between overhauls (TBO) was typically 650–800 hours depending on use.[25][26] By then single-stage engines had accumulated 2,615,000 engine hours in civil operation, and two-stage engines 1,169,000.[27]
I seem to recall that "transport banks" were favoured for the race-prepared Merlins at Reno as they had much better longevity - allied with Allison con rods which had the same stroke as the RR parts but seemed better suited to the abuse!