Happy New Year Everyone! Hope you all had a great party! 8)
Well as the US paper says there is no specific figures available, but from impression the stocks (fuel stocks in airfields in Northern Italy and Souther Germany it seems that the ratio of stocks was 50-50%, or perhaps 60-40% for C-3, so it appears that the 'roughly 2/3s of late avgas production was C-3' statement is definietely correct.
What is interesting is that Germans preferred supply their Italian allies with high grade C-3 avgas instead of lower grade B-4 (though both would be suitable for their use) and that some of the German bomber units towards the end of the war was only supplied with C-3; just as curious as the case of why the Italians were supplied with the high grade fuel (C-3 from about 1943 was equivalent 150 grade avgas), as none of the bomber engines actually took advantage of it; certainly not any of the Jumo engines used in late He 111s...
From early 1945 DB notes of meetings it appears that there was a tendency that fighter units in the East relied on B-4, and fighter units in the West relied on C-3, where possible (basically this means Bf 109G/Ks and the FW 190D, which could use either fuel, while the FW 190A/F types always needed C-3).
http://kurfurst.org/Engine/Boostclearances/DB_Niederschrift6730_DB605DBDC_20-1-45.pdf
Kurfrst - OKL, GdJ-Grp. Qu-, Br. B. Nr. 1561/45 g.Kdos. von 20. Mrz 1945.
Basically by the start of 1944 all Bf 109s with methanol boost would use C-3 grade avgas as a rule. The reason for this was probably that in case of failure in the water injection system, C-3 had high enough octane rating to do without knocking, while B-4 would lead to engine damage in this case (though
B-4 with methanol water injection allowed the same boost just as fine, so it was probably a safety measure).
The exception being the Bf 109G-10 and K-4 with the DB 605D engine which would need C-3 if they were to use of higher boost pressures; it would appear that they used both fuels. See my findings at :
Kurfrst - OKL, GdJ-Grp. Qu-, Br. B. Nr. 1561/45 g.Kdos. von 20. Mrz 1945.