Only the original Model 299 prototype used the Hornet S1E-G (R-1690), which was a supercharged
engine, thus the 'S' in the model designator. The follow on Model 299B (YB-17, Y1B-17) used the
SGR-1820-39, again a supercharged engine.
Y1B-17A c/n 1897 serial 37-369 was originally ordered as a non-flying test aurframe, but the order
to convert it as a flying aircraft was issued May 12, 1937. It was primarily used as the
Model 299F(Y1B-17A) as a test-bed for development of the turbo-supercharger installation
with R-1820-51 engines.
The Model 294 (XB-15) wing planform would convey no aerodynamic benefit.
If you really want to 'Lanc o' Mossie-ize' a B-17 then use the high-wing layout of the Model 299J proposal;
skip the trike gear; add a long, shallow bomb-bay; give it a raised Mossie-ish canopy; and reconfigure
the tail for a rear gun/turret.
... anybody else see the Betty in the upper left profile sketch?