I have gathered some of the info in an article earlier. Some new data has been found ever since, and it seems the initial Gruppe of Emils were belonging to II/JG 26, and as per Caldwell's diary, they seem to have received them in July 1940 during a refit (he does not say /Ns but he mentions the aircraft were new ones).
http://kurfurst.org/Engine/DB60x/DB6...asheets_N.html
German 100 octane / DB 601N fittings can be summarized as follows, via Mankau/Petrick's excellent Zestorer monograph. Essentially 110s had priority for these engines until the automn of 1940, when the situation reversed and 109s received priority and began to appear in larger numbers.
On the 12 July 1940 General der Luftwaffe meeting, it was noted that DB 601N engines are to be installed primarly into Bf 110s, then its followed in the serial production Bf 109E.
On the 19 July 1940 General der Luftwaffe meeting, it was noted DB 601N engine are installed in frontline Bf 110s. So far 1 Gruppe of Bf 109E was fitted with the new engine. The Bf 109F entering production is also using the 601N engine.
On the 26 July 1940 General der Luftwaffe meeting, the General Staff requesting more Bf 110 to be fitted with DB 601N. Decision would be made in the end of August 1940.
On the 9 August 1940 General der Luftwaffe meeting, it was noted that 3 Gruppen of Bf 110 and one Gruppe of Bf 109 was fitted with DB 601N. Increased installations require increasing the reserve of DB 601N motors.
On the 30 August 1940 General der Luftwaffe meeting, it was noted that for 280 'active' DB 601N motors, the no. engines in reserve is to reach 180.
On the 27 September 1940 General der Luftwaffe meeting, it was noted that the Chief of Staff decided that 4 Gruppen of Bf 110 is to be fitted with 601N and the number to be maintained. 1/3 of the remaining DB 601N engines is to be reserved as replacement engines for frontline units, and the remaining 2/3s are to be released to be installed in Bf 109 aircraft.
On the 18 October 1940 General der Luftwaffe meeting, it was noted that apart from the already present 1 Bf 109 Gruppe with DB 601N, no more is possible to be equipped. Existing DB 601N are required by: 1, New production Bf 109F 2, New production Bf 110 delivered by Mtt AG as replacement to the existing 4 Bf 110 Gruppen with 601N 3, 40 replacement Bf 109E (conversions) to maintain the strenght of the 1 Bf 109 Gruppe with 601N. 5, Replacement/reserve engines for 1, 2, and 3.
On the 26 October 1940 General der Luftwaffe meeting, it was noted that by the end of October, 1100-1200 DB 601N engines were delivered, and were used for the 4 Gruppen of Bf 110 and one Gruppe of Bf 109 equipped with DB 601N, and to maintain these units with replacements, and furthermore to recon units under Luftwaffe High Command. The remaining engines are used for Bf 109F-1, F-2 production. 130 engines were reserved for circulation (replacement). All Bf 110s produced, apart from the DB 601N equipped ones by Mtt AG are to be directed to maintain the strenght of 120 of night fighter units.
On the 6 November 1940 General der Luftwaffe meeting, it was noted that General Staff requested all DB 601N engines to be installed in Bf 109E. In order to free up engines, 2 months worth of production (November, December) of Bf 110s produced by Mtt is to engined with DB 601A instead of 601N. 601N engines are to be distributed: 1) Final production series of Bf 109E 2) Replacement engines for III/ZG 26, Erpobunggruppe 210. If 601N engines are not available in sufficient quantities, the following Gruppen can be given 601A as replacement engines: II/ZG 26, II/ZG 76. As the production of 601N in January 1941 will be considerably greater, Bf 110 production shall switch completely to 601N.
On the 22 January 1941 General der Luftwaffe meeting, it was reported that on 1 January 1941, the following number of DB 601N engines were installed in frontline aircraft.
in Bf 109s
Bf 109E-1 : 16 pcs, Bf 109E-3 : 1 pc, Bf 109E-4 : 54 pcs, Bf 109E-6 : 1 pc, Bf 109E-7 : 34 pcs, Bf 109E-8 : 2pcs. Bf 109F-1 : 5 pcs.
Total 112 Bf 109E with DB 601N present in service, plus 5 Bf 109F.
in Bf 110s
Bf 110C-1 : 4 pcs, Bf 110C-4 : 40 pcs, Bf 110C-5 : 12, Bf 110C-7 : 14 pcs, Bf 110D-0 : 18 pcs, Bf 110D-2 : 20 pcs, Bf 110D-3 : 8 pcs, BF 110E-1 : 176 pcs, Bf 110E-2 : 14 pcs.
Total : 306 engines, ie. 153 Bf 110s with DB 601N present in service.
in Misc. types
He 111P : 8 pcs, Do 215 : 68 pcs.
By 1st April, the following conversion to DB 601N is planned: 6 Gruppen of Bf 110 = 480 engines, 5 Gruppen of Bf 109E-7/N = 200 engines, 12 Gruppen of Bf 109F = 480 engines, 'Rowehl' = 70 engines. This means by 1 April appx. 850 DB 601N engines will be in active operation.
etc.
Source: Pages 24-29 in Heinz Mankau/Peter Petrick : Messerschmidt Bf 110, Me 210, Me 410. Aviatic Verlag, 2001. ISBN: 3925505628