New user here and excited to try and soak up as much knowledge as yall are willing to give. I have recently acquired an early M4 complete airframe and wings (skeletonized) as well as a bent M5 fuselage (mostly complete). Looking over the FAA 51% stuff, it seems the consensus is that the fuselage or the wings must be scratch built to meet that criteria, or some combination of the two. My mission for the airplane is a 4 place, with cargo family plane. No long CC, mostly 100-200nm trips to unimproved airstrips. We are a taller family (6'3" 240, wife is 5'9" with two boys under the age of 5 at the moment). I am planning on mounting an R-680 on the nose, which is considerably heavier than a IO-540. I am looking for any insights for fuselage strengthening (wouldnt mind making it longer and wider if necessary), wing design/rebuilding to carry the extra weight, and any upgrades to the overall gross of the airframe. In a perfect world I would want 1100 useful when complete. Too ambitious? What are some thoughts?

That might be a bit of a tough combo to pull off. Getting to 1100 LB use load is in theory possible with the M5, dont know if you could do that with the M4. going to a heavier motor will make the weight and balance extremely difficult, let alone the affect on use full load. Given what you are wanting out of it, a Moose might be a better fit....

If you pull it off, I would love to see a build on something like that!

This would be cool to see! A Maule with a radial engine!
What part of the country are you located?

Dale Smith - Im thinking lengthening/widening the fuselage and obviously going with more wing area to help offset some of the nose weight while also allowing more cabin room and beefing up. I looked hard at the moose, theyre hard to find on the used market and kits pop up occasionally, but the Maule kinda caught my eye as being a very modular airframe with tons of potential for add ons. Combine that with a radial that fell into my path and here we are. We will make it all work though, something about a radial on the front just makes me smile

HeavyLoad I am about an hour west of Fort Worth