I'm currently building a GP Skybolt kit, the second one I've done since the first met an untimely end. The kit's an old design, pre-dating 3D and builds heavy, especially tail heavy, and there's not much you can do about making the tail lighter without compromising strength which leaves most of these planes carting useless lead around in the nose.

Currently the fuse is 90% complete, and the engine (saito 1.25) is mounted. The cowl for these is a 2 part affair (front & rear halves) which needs to be cut down to size & glued together. I've done the cowl, but rather than cutting on the supplied "cut here" lines I just trimmed off the flashing from the rear half, leaving the cowl almost 1/2" longer than standard. I was measuring it all up last night, working out how much I needed to trim from the cowl when it occured to me that I could just put a thick ply block behind the engine mount, moving the engine forward about 1/2", and reducing the required lead.

The kit actually omes with 3 such blocks, intended for use with smaller 2 stroke engines, so I can't see any mechanical problem with it My question is will moving the thrust (prop location) forward of it's standard position alter the geometry, dynamics, balance etc of the plane? My suspicion is that it will be fine but theres more that I don't know about aircraft design than there is that I do.