I'm just getting started with this winter's build, a Jack Stafford Aircoupe (by Leisure RC Models), and although the laser cutting is incredible, the kit is an old kit and the plans/instructions leave a lot to be desired (I've built a good number of kits over the years, Goldberg, Top Flite, Balsa USA, Sig but those all have three photos for every step, this one is pretty much glue/cover/fly, so I think it'll take most of the winter to just figure things out).

But back to the firewall. The plans (one sheet, and I'm not sure how close "to scale" it is) shows the distance from the front of the firewall to the back of the engine backplate as 3 1/2". When I mount my Saito 62 I have a firewall to engine backplate of 4 3/4". Sounds simple enough, move the firewall back 1 1/4". Is it really that simple? If it is, it'll be the first simple thing I've ever come across in this hobby. Advice anyone? Anything else that needs to be considered? Balance point?

Homer the balance C.G. does not change moving the fire wall back. Best way I found to move a fire wall is redraw where it needs to be on the plans. Mount or standoffs need to be on the engine, then set it on the plan so the back of prop is 1/16" ahead of the cowling or the place its shown on the plans. Square the engine up as close as possible and mark the back of the mount on the plans, that will be the face of the new location of the fire wall.

Leroy

Some people will move the entire firewall back, others counter sink a box..
I even know of guys that will leave the firewall alone and move the cowl forward a bit and build in between the two...

I would take into consideration mostly how the access to your motor is affected for upkeep and adjustments..

Any of those will work.. As long as the CG is right it should fly fine. Where the fire wall is at makes little difference.