RE: LR-1 Pylon racer
Mathyoo, if I only had the GP.42 , then I'd go ahead and install it using the smallest .40 size engine mount I can find.
The GP.42 is not exactly a speed engine, but it'll fly the LR-1 pretty fast if you can balance the plane. I'd try a 9x7 or a 9x8.
The good thing about installing the GP.42 is that later you can drop in a good SPEED .40 engine for some REALLY fast flying without re-doing the engine mount.
I'm on the look out for a used Jett or Nelson quickee engine (as long as it has a carb, I don't want to fly full bore all the time)
I'm figuring that if my electric version is flying ok at over 4 lbs, then I can go to a .40 glow even if I need to add a couple of oz to the tail to balance.
IMO, the LR-1 is a pretty stout airframe overall. The wings don't take crash loads very well, but seems to hold up fine in the air.