Sounds like a run project !! Gotta watch this one.

90L Engine would be a heck of a match The SJ-90L and 90LX are available as both side and rear exhaust. These are physically the same size as current OS61/91 engines.

The tetra tank Bobber noted is worth considering - relieves 99% of your fuel system worries.

Worth noting, there were many, many people who flew pattern with non-pumped fuel systesm for a LOT of years. Maybe a handful of K&B LEE engines with pumps for a while. YS was the only pumped/pressure/regulated system starting in the early 80s. The OS pumper didnt show up until the late 80s.

Rossi, OS 61FSR, Webra Speed, OPS, CMB - there were no pumps needed. The tank pressure provided by a tuned pipe is substantial - beyond what most stock mufflers provide. The pump also added complexity and a point of failure. A pump is only really needed when you are trying to deliver a lot of fuel (energy, make power) at lower RPM and lower throttle settings, or you have to transport the fuel a long distance.

The idea of putting the tank aft for CG reasons didnt come around until the pattern ships grew big/fat enough and folks started sicking servos outside of the airframe so you could actually fit one that far back