If you plan on replacing your rod holders/braces, I'm happy to send you the ones I had made before deciding to go with Starboard. 3/4" ACX ply sealed with 2 part epoxy. I never got around to finishing them up with the sanding and painting, but they are all cut to fit and ready for finishing.
I always trash the deck joiners and use doublers to secure the different sections together, just need to remain mindful of the stringer placements.
For steering, I replaced mine with a Seastar NFB 4.2
I've seen both, one continuous piece that wraps around the bow, and two separate pieces that terminate at the bow under the cap. I've always re-used the inserts, never had to install new. they rivet to the channel at each end termination and sometimes are a bear to stretch/pull to line up with...
You could still remove the splashwell and leave the transom in. I guess it depends on how thorough you want to get with everything. If the decking is in need, I'd be willing to bet your transom is no longer at 100%. Now would be the time to do it, but it all depends on what your timeline and end...
The only solids are the ones attaching those lower side braces(below the rod holders) to the side of the hull. The flat panels behind them, along with those supports under the splashwell, are blind rivets and screws. No solids, no welding. They have screws into the deck, blind rivets into that...
I think you'll be just fine with a 115hp on a 21' Mariner. They are not heavy hulls and the old 115hp 2-strokes are much lighter than the current 4-strokes. Prop it correctly for your needs and you'll be just fine.
I have a 115hp sitting here waiting to go on my 18' MR and its the max rating...
You can still find the rub rail, but it's not cheap. If it's not too far gone, I found the easiest way to reinstall them is soak the rubber in a big 5 gallon bucket or storage tub filled with hot water and some dish soap. It will make it more pliable and lubricated. Feed it into the rail...
I went with a dedicated ATS 4X rivet gun. I've used a standard air hammer in the past and its fine for setting one or two, but well worth picking up an actual rivet gun if you have several solids to drive.
As noted above, center punch the head of the old rivet, drill off the head as you would...
I went down this same road with my MR180, only way to do it right is to completely remove the side supports and rear panels. The front deck panels also had solids through the hull. I took the opportunity to purchase me a new rivet gun for setting the solids :) You'll also likely find some...
They all have foam, just a matter of what kind of foam is in your '82. My '84 had poured foam in the hull and the white Styrofoam board under the gunnels and behind the panels. I'd assume your '82 would be somewhat similar.
I'd personally stay away from the pour in foam and use the foam sheets. If yours is leaking, and has water trapped in the hull, you're likely to find corrosion and possibly even pin holes through the hull where you remove the original saturated foam. Look for spots like the picture attached on...
