It should not change all that much, I'll bet. If you look at that heavy
engine moving a few inches, and the increased cowl area in front of
aerodynamic center pressure, then look at that long, long arm back to the
fin and rudder, it should only take about a third of the area the engine
added to make it all work out. Increase the fin/rudder height a couple
inches, or add a small dorsal fin, and all will be well in the world. :-

It will change it some. My Jodel came out considerably heavier
than designed, mostly to the use of birch instead of the mahogany
specified in the original French drawings, fabric over all ply surfaces
to meet Canadian requirements, a tailwheel insterad of a skid, and so
on. Since most of the added weight is behind the CG, it was tailheavy
and the engine had to go 11" further forward.
The longer nose side area results in a little less directional
stability with the same tail, and I won't spin it because I don't know
just what the effect of the extra weight in the tail (and the longer
nose arm to balance it) might do to the spin; it might flatten into an
unrecoverable situation. Sure does an awesome slip, though.

Dan