Let's install it in something now. Bf 109 - no. Bf 110 - again, no I'm afraid, not unless a major redesign is done, paying a hefty price in weight. How much of fuel for thirstier engines? After all is said and done, we're maybe at 350 mph - good, but no cigar. Less Bf 110 produced than historically.
The Do-17 will not became Do 217 with DB 603 instaled, again the major redesign is needed, that means delays in production, that means less Dorniers for BoB.
He 111? That might be a good idea, the bomber will still be slow-ish, but not that slow, still needs escort.
Ju 88 with bombs hanging out is still slow to go without escort.
UK is already out-producing Germany in 1940 in engines, can the Germans trade a small lot of DB 603s produced for a bigger lot of DB 601 that are not produced?
I'd agree with Wiking - for the LW's victory in the BoB, a whole new mental set-up is needed (escort policy, target prioritization, not thinking that after France is defeated you don't need increase in production, also more pilots are needed). As a technicality, have all of the Bf 109s outfitted with drop tanks, that would've meant plenty of problems for RAF, and have Bf 110s employed as low-level fast bombers.