You have the hardest part to find. The magneto plate from the 7.5 hp KE4 & Mark7 is the same as the 10 hp. magneto. They are plentiful and not expensive. The control handle from your Scintilla plate will work. Now the flywheel. They do come up for sale from time to time but are expensive. I know of one but its $125.00 + $14.00 shipping. I will PM you the contact info if your interested and the email of a member who I’m pretty sure has a plate to sell you. However if your making this change because your motor became harder to start, then the bottom cylinder started dropping out, and now it wont run at all, changes the crankshafts seals (epically the lower one) before you spend any more money.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.