for the 1939 Suizei class of bombers is that only 2 countries had a 1000hp/15,000ft engine. a few others had works in progress. and there were few hiccups.
Britain, got the 1000hp engine, doesn't have enough propellers or at least good ones.
Britain had no problems in installing the good propellers on their bombers, so they should be okay. There is a lot of dead or obsolescent
wood around that deserves the axe, so our brave new fast bomber materializes.
France, no 1000hp engine, working on it.
Italy, no 1000hp engine.
Japan, no 1000 hp engine (license signed in 1938, Prototype D4Ys used imported DB 600s in 1941, production planes in 1942, a little late)
Soviet Union. M-103s or a handful of M-104s? According to one source 50 M-105s built by the end of 1940.
US, 1000hp engine in 1939? got the design, got 40 engines by New Years Day 1940. rebuilding several hundred engines in the summer/fall of 1940 to meet spec.
France, Italy and USA can try with the V12s they have, and concurrently have the versions with the 1000 HP radials in the nose.
(BTW - anyone knows why the much smaller MB.152 was that much slower than the Re.2000, despite both having the similar engine with similar power? was it because the prop shaft was skewed against the aircraft datum line?)
Yes, this is a workaround so there is a fast-ish bomber until the V12-powered version is, hopefully, around; not really 320-330 mph turn of speed, but already ~300 mph is a boon when compared with light bombers these countries had in production in 1939-40.
Yes, Soviets have probably the best bet in the M-103.
With 1000hp engines there is only so much trading off you can do. With 1300-1400hp engines you can do a lot more because a lot of you other "payload" is the same.
Two man crew (?) 200kg, cockpit structure, instruments, 50-70kg of radio gear, rear gun? crew armor.
All the same for the 1000hp plane and the 1400hp plane (or mostly) so you have more power to get the bombs and fuel off the ground even if you use a bit bigger wing.
Trick with 1300-1400 HP engines is that it took a while for these to became available in good numbers and reliable for 1-engine multi-hour tasks. We can retrofit a lot of these engines in the legacy airframes, though, so I'd still suggest that 1st go is with 1000 HP types, so these can be had early in the war.
US has the best chance at a semi fast radial engine bomber
The R-1830 offers about 1000hp at 14,500ft with a two speed supercharger and some abuse to the engine. At least the engine is under 50 in (1.27m). A 55in radial engine has about 20% more frontal area.
Americans can mimic what they did with when the DB-7 morphed into the A-20: start with R-1830, with a quick follow-up with the R-2600. Re-engining it with a V-1710 - P-36 into P-40 style - is also an option.
Or, start with the R-2600 from the get go, and re-engine it with the R-2800 when this engine is available. Obviously, the second type will start as a bigger A/C than the 1st type, perhaps 280-300 sq ft vs. 250-270 sq ft?
Also the rate of progress for somethings was rather quick in some ways and not so quick in others. It took about about 8 years for the US to go from installing flaps on the P-26 to the Douglas A-26 flying with double slotted flaps (another 2 years to go into service). Sometimes if you start too early you are stuck with old airfoils, structures and systems.
Americans were making wings for military aircraft in 15-16% t-t-c ratio (root) before 1939, and were also using newer airfoils. This is fine for the whole war.
Lockheed have had Fowler flaps in service by late 1937, so there is a precedent for these.