Comments/Advice on outboard mounting plan

[brownoarsman]

Hi everyone - due to a recent diesel engine breakdown I'm installing an outboard on the back of my Pearson 28 until I get back to Maryland and can either repower or repair/rebuild with the comforts of home (i.e. air-conditioned work room). Until then, I'll need to install an outboard to get me home, and I'm aware of the disadvantages of doing so (gasoline on board, chop that could lift the outboard prop out of the water, insufficient power at the worst time, no high-power alternator, etc.). While I worked in home construction when I was younger, this will be my first time installing something major on a boat, so just wanted to check on my method.
I've included a photo of the stern of the boat. The distance from the bottom of the transom to the water is 7", and the distance from the bottom of the transom to the top of the transom is 32". The transom has a slight angle towards the bow on the way up. You'll notice that the rudder comes all the way to the edge of the transom.
I'll be using this mount which has 11.5" travel. I had thought the goal with an outboard mounting was to get the prop as low in the water as possible without submerging the powerhead to reduce the chances of it popping out in a head sea. However, Garelick actually recommends against this, and would prefer that the outboard is mounted such that when the bracket is in the up position, the cavitation plate is basically at water level. This would seem to make a long-shaft outboard a bit ridiculous, as if one follows Garelick's instructions, for every inch added to shaft length (measured from the top of the mounting clamps to the cavitation plate), one would just move the mounting position up an inch. Could anyone please tell me what I'm getting wrong?
As far as the installation, my plan is to install it on the centerline of the boat. The bracket should hold the outboard about six inches away from the rudder when in the down position - will this be far enough away from the trailing edge of the rudder that the turbulence introduced by the prop doesn't disturb the water flow over the rudder?
As far as the actual manual labor - I'll remove the swim ladder, sand inside the swim ladder bolt holes with a bit of rolled up sandpaper, brush it with toluene, wait for the toluene to dry, plug the back of those holes with cotton balls soaked in epoxy, brush neat epoxy around the inside of the hole, and then fill the holes with thickened epoxy/hardener. I probably won't sand it down at all, because I hope to reinstall the swim ladder later! And what's a little unfinished transom among friends.
To install the outboard bracket, once determining the appropriate position, I'll drill 3/8" holes perpendicularly to the transom, clean them out with toluene, wash the inner and outer mating surfaces of the transom with toluene, apply 4200 to the mating surface of the bracket and to the mating surface of a square of 1/4" aluminum or stainless steel, dollop a bit of 4200 inside the bolt holes, and then tighten everything together with 5/16" hardware (bolt, washer, nut) as per Garelick's recommendation. I don't quite understand why one would drill 3/8" holes for 5/16" hardware, and perhaps someone could explain that to me as well.
How does this all sound? Thanks!
Dan