Like many ex-military Cubs I suspect yours either incorporates parts from several airframes or has been the victim of a paperwork mix-up — very common with ex-French L-4s. Records for the original French civil identity F-BDTM show it as factory serial no. 9542 and its USAAF serial as 43-681, both of which would fit with it being a 1942-built L-4B. However its later registration F-BGPS is shown in some sources as factory serial no. 12544/44-80248, which is an L-4J, and yet another frame no. 12374 (also an L-4J) has been quoted, possibly suggesting a replacement fuselage. I've also seen the USAAF serial 43-28251 quoted for this aircraft, but so far as I can tell that wasn't a Cub of any sort!
I'd strongly recommend you join the Vintage Piper Aircraft Club, whose members include many J-3/L-4 owners. Secretary Roger Peperell and his colleague Colin Smith are the acknowledged world experts on the histories of Pipers. Colin, in particular, has exhaustive records of L-4s/J-3s and should be able to set you straight (Roger Peperell, VPAC, 51 Church Street, Kidlington, Oxford OX5 2BA, e-mail:
[email protected]). You should also get hold of a copy of Ken Wakefield's classic but out-of-print book 'The Fighting Grasshoppers', published by Midland Counties Publications in 1990, ISBN0-904597-78-4. It is packed with information and photographs about wartime L-4 operations, and has details of colour schemes etc. Can't locate Ken's contact details at the moment, but when I do I'll post here — he's The Man when it comes to L-4 and liaison aircraft lore.