IMPORTANT (if you use my pad design for outboard bracket) The short shaft engines, both seagull and modern, are designed to work with transom depth of around 15″. This means that when you put on a bracket the top of the pad (to fasten the engine to) should be roughly the same height as the transom. When fitted as per my drawing/description you cannot have any of the plywood extending above the part of the bracket that the engine fastens to or the engine will be too high
I use a fixed mounting that bolts to the pad (no thumbscrews) so that the engine is the same height as it would have been on the transom.
If you too use a seagull you could buy a similar bracket (though they are rare) or modify the normal mounting by taking off the thumbscrews and bolting on your existing mounting
If you use a modern engine and you need to extend the height of the plywood pad to get the engine on you could alter the rake of the extension bar to get the engine level. A welding/fabrication shop would do this cheaply and it will work just as well horizontal of even pointing down. You can get the engine height exactly right
If anyone is confused please contact me and I will telephone you to explain.