Thing to note might be that German V12s were in general better engines than the Soviet V12s, if we look at combination of power at any altitude, weight penalty, and reliability. The VK-107 and -108 were very unreliable, and very late.
As Tomo has noted, very late. The VK-106 and VK-107 were in development in 1940. Then things get grey. They don't get developed in time forcing continued use of the VK-105. Even in 1946 production is stopped and restarted due to production/quality problems. Most sources don't say much more than that. I have no idea if in peace time they wanted better reliability/engine life over what they accepted in war time or if the new engines didn't mean wartime standards. If you are having trouble in 1946 the chances of them being useful in 1944 are about nil.
If Germans can have G&R start making the 14R, that can help to turn the weight spiral of the complete aircraft down, too.
Again the GR 14R is sort of vaporware.
1944 book (and who knows were they got the information, the forward was written in Jan 1944 so the GR factory was still in German hands and would be for months)
gives the following.
Displacement..................38.7 L
CR........................................6.8 : 1
Supercharger ratios.....6.5 : 1
............................................9.0 : 1
Weight.............................1805lbs
fuel rating.........................92 octane
BMEP.................................213lb/sq/in
take-off.............................1590hp/2600rpm/46.5in(1180mm) hg boost
rated power.....................1,660hp/2600rpm/3300ft(1000m)
..............................................1,580hp/2600rpm/16400ft(5000m)
Cruise.................................1,320hp/2400rpm/6,900ft(2100m)
...............................................1,230hp/2400rpm/19,700ft(6000m)
Take-off power is done with 100 octane gasoline.
The power down low
might be do-able.
The power in high gear is pretty unbelievable. That has got to be about the best 2 speed supercharger ever built.
Find another engine that gains 13,100ft (4000meters) and still makes 95% of its best low gear power.
They kept claiming similar high altitude power in the post war years.
I have no information on what kind of wonder supercharger they were using, like a Szydlowsky-Planiol or something else?