I agree with Foodstick that it probably won't make that much difference. I have lowered the engine on sport planes to get the carb closer to the fuel tank centerline without any significant impact on handling. The thing you do have to keep an eye out for is prop clearance. The semi symmetrical wing won't be as likely to balloon under power the way a flat bottom wing would. The amount of right trim shouldn't need to change. I would suggest keeping the incidences per the plans for this particular airplane. The modification of incidences and addition of down thrust is an issue with the BUSA WWI biplanes of similar size due to their flat bottomed wings. Due to their layout a lot of WWI planes have a center of drag that is higher than the thrust line. This tends to lever the nose up under power. With the Phaeton your wings are relatively close together and the airfoil is more tolerant in this regard. Good luck with your build.