I agree Denniss,
but two points:
The basics for the pressurized water cooling came frome the record engines between 1937-1939 and,
I think without the DB 604 and the coupled stuff DB 606 etc., it was possible for Daimler to develop the DB 603 from 1937 till 1942 ready for mass production and near the same performance and reliability as the DB 603 from end of 1943
Well the DB604 might have kept the Junkers Ju 288 program going, it was a very powerful engine. From my understanding it didn't suffer the reliability issues of the Jumo 222 but had inferior fuel consumption and cruise power despite having the same top power. I really don't know of any single engined fighters ever designed for its use but imagine it would be possible.
Piston engine development in WW2 took some 6 years. You can see that in every major engine program eg R-3350.
The DB603 was slated on the production plans in 1944 in the form of the Fw 190D-14 (DB603EM) and Fw 190D-15 (DB603LA). As far as I know the Fw 190D-9 was essentially a modified Fw 190A-9 with a new firewall for mounting the Jumo 213A and a plug in the tail to lengthen it by 20cm. The Jumo 213A was a 1750hp bomber engine that needed several power boosting methods to make it competitive which were in fact installed basically rich mixture injection to get to 1900hp and then various forms of MW-50 either injected or blown in. The proper Jumo 213 for fighters was actually to be the Jumo 213C which used C-3 fuel from the get go for 1900hp and had mountings for a hollow prop shaft so as to be able to fire a motor canon. (the Jumo 213A was surplus bomber production which is why there was no motor canon on the Fw 190D-9 only the rare Fw 190D-13)
The DB603 engine the Germans had available in 1942 was the DB603A which produced 1750hp and was used on the Me 410, Dornier Do 217M and some prototypes. The fighter version was supposed to be the DB603G which was a C-3 fuel burning fighter engine of 1900hp.
Broadly the engines the Germans had was
DB603A 1750hp (saw service) critical altitude 5500m used 87 octane B4.
DB603AA 1600hp sea level but higher critical altitude (about 8000m) saw service likely in He 219, Used 87 octane B-4 fuel.
DB603G 1900hp but used C3 fuel to achieve this. Seems to have been used on prototypes but never entered production.
DB603E 1800hp advanced engine which combined the low altitude performance of the DB603A with the high altitude capability of the DB603AA. Might have seen service in He 219 and Do 335 but very limited. Used 87 octane B-4 fuel.
DB603EM version of the DB603E which could produce 2250hp through the combined use of MW-50 and C3 fuel. The allied oil campaign seems to have made the Luftwaffe fearful of continuity of its C-3 fuel supply and so production of this engine was cancelled. Otherwise the Ta 152C-1 would have entered service before the Jumo 213E-1 powered Ta 152H.
The DB603L engine added a two stage supercharger, a variant of this, the DB603LA which had lacked the larger inter-cooler of the DB603L was what actually entered service in the Ta 152C-3 because it could do the job without the C-3 fuel on only B-4 fuel while the two stage supercharger gave better high altitude performance as well.
The DB603N had a more elaborate two stage infinitely variable driver supercharger with two mechanical gear speeds. It was to use C3 fuel to achieve 2800hp but of course never entered service.
As far as I can see a Fw 190D-5 modified from a Fw 190A-5 airframe should have been possible in 1942/43: interesting to me is the use of the DB603AA engine which might have given a good interim high altitude fighter. This is where the Germans were caught out as USAAF raids came in at high altitude and aircraft such as the P-38, P-47 and P-51 had much better engines for fighting at 22,000ft+.
The other dark horse is the DB603G. I suspect that issues with the DB603G were one of the key reasons the Me 309 was abandoned as Messerschmidt was forced to experiment with the much weaker DB605.