BMW 801's are too big (the Ha-102 is *really *small!), and IMHO also not right from a timeframe point of view - at least for me, it's whifworld, after all.

I also already checked the option of Jumos from a Ju 88, and they are too big/wide, too. In desperation I also checked the weird radial Jumos from the Frog He 219, but they are a) ugly and b) also too wide. DB601s are a bit narrow, but they would look plausible on the slender aircraft and fall into the right time frame. Gotta dig further...

BMW 801c:

Length: 2,006 mm (79 in)

Diameter: 1,290 mm (51 in)

Dry weight: 1,012 kg (2,226 lb)

Power output: 1,560 PS (1,539 hp, 1,147 kW) at 2,700 rpm for takeoff at sea level

Ha-102

Diameter: 1,118 mm (44.0 in)

Dry weight: 540 kg (1,190 lb)

Power output: 875 horsepower (652 kW), 2540 rpm at takeoff,

925 horsepower (690 kW), 2450 rpm at 1,800 metres (5,900 ft)

The BMW 801 is only some 4 inches greater in diameter and weighs twice as much. However you get nearly twice the horsepower. Haven't been able to find much on the Ha-102 though, so it isn't inconceivable as a replacement.