You’re a little further ahead in your conversion. I’m amazed I found your post, I’m doing the same conversion, same boat design, and live in the same area. I think by using two knee braces on each upper corner of the bracket bolt pattern there should be minimal torque movement to the transom. Outside the center transom it is only one layer of plywood/fiberglass with 1 1/4' thickness. As you noticed the center of my transom is two layers of 3/4' plywood with 1/4' fiberglass on each side for a total of about 2' thick. I think the 2' x 2' x 3/8' aluminum angle will be stronger than one made of plywood. Naturewaterboy, I decided to use metal knee braces because I had read about others using them and also it allows me to connect directly to the bolts that fasten the outboard bracket. Wiring harness for new engine with some new instruments. Hydraulic steering installation (was not required, but thought it would be cleaner installation that rigid cable). I estimate another 3-4 weeks before I do some testing in the water. I also need to have them welded in a few spots for extra strength. It is not difficult, just time consuming to get precise angles cut/bent using only hacksaw and bench vice. I am nearing completion of the knee braces and will post some photos soon. I do not understand the advantage of extending 500+lbs over 2 feet aft of the transom. If it were my boat, i would repair the I/O hole in the transom, make a cutout for the outboard, beef up the corners of the transom by fabricating (a splashwell with) intercostals that attach the transom to the sides on a lateral plane. Personal opinion, i wouldn't use the bracket- it exaggerates the moment of the hull beyond it's design takes the most substantial weight in the boat (the engine) and moves it aft a good 4ft of the original hull design.That bracket is going to apply a leverage the transom that it has never experienced. it wouldn't hurt to make the plates, as large as you can make them in order to capture and tie into more of the existing structure-it's all about distribution of the load, as you well know. Have as many bolts as you can, grip the bracket and both plates. I like the braces in #6 that tie in your transom to the stringers, but in order to get the maximum benefit from those braces, you should coordinate the holes in the O/B bracket, both inside and outside plates, AND the braces. The old I/O was bolted to the stringers which took a major load off the transom. With the I/O, the load was never directly on the transom as it will be with your bracket. the entire transom must become, in effect, a solid piece as it was before the original cut out for the I/O. It is not good enough to simply fill the hole. Unless the plug is integral to the transom (multi-layered glass faired on the inside and out), you will still have a hole on your transom.You want the additional load of the engine to transition past the hole, not be drawn directly to it. This is just a rough drawing of the brace, it will actually wrap more around the stringers with bolts through the stringer side and top. Brace will be in tension since forces on the top of the outboard bracket are pulling outward. Photo5-Proposed I/O plug and stainless plate over inside transom I/O hole. Photo4-Inside transom showing existing construction layout. Photo3-Proposed stainless plate mounted outside over I/O hole. Bolts are in new holes for outboard bracket. Photo2-Outside transom showing hole where old I/O was mounted. Photo1-Outboard bracket temporarily bolted to transom. Question2: Can I use marine grade aluminum instead of stainless steel for the plates and knee brace? (much cheaper and easier to work with) I plan on using 3M 5200 sealant wherever metal contacts fiberglass. I hope to minimize any transom flexing by using a knee brace that is attached to the top Bracket bolts and the stringers in the bottom of the boat. The outside/inside transom plates are primarily to ensure that the plug stays in place and remains watertight, the inside plate also serves as backing reinforcement for the bracket bolts. The sequence of photos show how I propose to mount the new engine. Outboard Bracket: 'Stainless Marine' 26' setback (20'high x 20'wide) 1/4' marine aluminum construction New Engine: Honda 150hp four-cycle outboard (already purchased) Old Engine: Volvo-Penta AQ125 I/O 120hp (already removed) I am seeking suggestions from those of you who have replaced an I/O engine with an Outboard on a bracket.

Inboard outboard motor diagram