[drgondog]

Andy - the question has variable answers that usually start with 'it depends on'....

For example mass wing changes on P-51's would not have been done in 'kit form' for Group or Wing Depots, while elevators were converted from fabric to metal on late model B's and D's after August 1944. Ditto up-locks for main gear doors and other structural mods to reduce structural failures from dives.

Having said that - a ship that started out as a P47-2RE remained a -2RE with engineering records to indicate what mods were installed to upgrade radios, props, trim tabs, elevator covering, canopies, etc., to 'convert to a -5.

Ditto P51's

For example, I'm not aware of 85 gallon fuselage tanks being installed in the field but someone else could shed light on that subject. And certainly no B/C's were converted to D's (major wing/fuselage changes).

The same applies to the P-47D's. When the D's got the tear drop canopy and wet wing - the older models were re-assigned to other groups or retired (to FTU or Group 'hacks') as the newer long range ships came into the inventory... and when the M's came in, the 56th was the only USAAF/ETO Group to get them - while they shipped out the -25's to Ninth AF Groups.