Nice Chieftain! Your adoption photos look so much like mine, same hull, engine, and Leaves!
Had a whole terrarium complete with ants going. Looks like you cleaned her right up proper. Other than losing the ol 302 dinosaur drive I like your plans of outboard bracket with swim platform. Thats the best realestate you can add if it doesn't have a platform already! W
Afterall what's a boat without water access? Doesn't seem goofy at all, make it to suite just how You'll enjoy it. Most people prefer outboards vs I/O these days and totally understand their reasons.
Now as for the 1" thick slab- I think that would be massive overkill unless you are needing protection from gunfire haha so maybe go lighter like 3/8 and it'd still be crazy strong. I don't want to insult you or your welder friend but there is caution to be taken if you decide to start welding a hull like this. It definitely was not intended to be and there are reasons why welded hulls are generally much thicker, all over, vs the thicknesses our vintage SC riveted boats run. Even an A+ land-based welder through no fault of their own would not be familiar with these sorts of issues typically.
Personally I'd stay with the original hull skin and add a new thicker plywood transom inside for vibration dampening and ease of installation. If bracket attached high and low it wouldnt need a 1" thick plate to lever off of. Its all about spreading out the load and the effects of leverage.
I did a lot of mods to the floor layout on mine and a lot of it had to do with wanting a simpler, more level floor like you.
One point of caution in your grand schemes is to keep in mind that like most boats in this size range these riveted hulls flex, quite a bit, and all the materials overlap and flex together in a semi compatible way. If you add something super rigid like a thick monolithic metal slab floor or transom you might have some tearing issues where, say, a much thinner more flexible material meets a way thicker much more rigid one. I had that issue before on another aluminum boat once. Just food for thought while planning your modifications for your future adventures.
Also, where possible, if you can rivet a welded assembly to the hull vs welding it helps it have that slight allowance for flex while also not putting too much heat into the original Starcraft hull. The OG hull has rubber like material sandwiched tight in the hull seams. If it gets hot it burns it up making a gap and the seam is no longer structurally sound. I have completely avoided welding to the thin aluminum hull myself. Partly for this reason.
I think you have an awesome starting point and a lot of decisions and also smiles ahead of you if you see it through and get her back out there. Lots of great help on this site. Best of luck to ya!
