[drgondog]

I am only speculating but it is possible that the vertical stabilizer ventral fin was added at the factory for the last series of P-51C-10 but for sure the last 20 P-51C-10's were converted at the factory for F6C-10 Recon. It is also possible that the -11 was the break from 1650-3 to 1650-7 Merlins. Whether or not they actually designated a -11 block is unknown to me. Gruenhagen has block 44-10753 thru 44-11152 as P-51C-10's

It is possible that there was a typo by Gruenhagen when he transitioned from Contract NA-103 (P-51C-1NT through P-51C-10 first award) to NA-111 where he references 400 more P-51C-10s built after the first block of 550 -10's. Having said that, the NA-111 was also the contact number for ALL of the P-51K's