With the kind permission of Apophenia, I present my take on a couple of inline powered T-6 racers:
First, real life: These two entered into the 1947 National Air Races Halle Race for women. Number 61 was the actual XAT-6E prototype. It was to be flown in the race by Margaret "Mickey" McGrath. In the 1947 race, Mickey either did not start or pulled out after 1 lap when her gear would not retract (depending on which source you choose to believe). Number 49 was built as a production AT-6D but modified for racing with a Ranger V-770). It was flown in the 1947 Halle Race by Dori Marland (Hollywood actress and former WASP squadron commander). Dori definitely started, but dropped out with engine problems after 3 laps.
Slide1 by
cacree, on Flickr
The second pic shows race number 61 as modified for the 1948 Halle Race - this is definitely NOT real world! Mickey McGrath had #61 modified with a single-seat cockpit, flying from the rear seat for better aerodynamics. The stock AT-6 windscreen was moved aft and fitted with a custom made blown plexiglass canopy. The only other modification was a fairing fitted to the tailwheel.
Slide2 by
cacree, on Flickr
Finally, in 1948, the two Ranger powered rivals met again, but with much more radical modifications. Number 61 now had a much more streamlined custom canopy fitted, and the vertical fin and rudder were both shortened to reduce drag. A retractable tailwheel from a P-51 was also fitted. Meanwhile, #49 received the entire tail unit from a P-51 (but with AT-6 horizontal surfaces in order to abide by Halle Race rules). Both aircraft were some 20-25 knots faster than any other AT-6 in the field and came first and second in the 1949 race, after which they were both banned by the simple expedient of writing a requirement for an R-1340 engine into the rules.
Slide3 by
cacree, on Flickr