The yammies are bang on maximum weight for the craft's transom 164kg. Roughly 82kg each, plus the heavy original steel a frame which stresses the transom ( as some people tow of it too ) yes the boat will eventually plane on one engine 13-15knts required to get on the plane.
The hole would need o be moved to the side and the original capped off, of course the 8 holes also need to be capped. Useful if you have a local shipwright to do it for you or tackle it yourself.
The transom will be cut lower to support the twin setup and there is no reason to change that as I have 2 pricing twin seariders ( 1 has been left and one has a brand new transom )
The blue boat has just been capped and has a long shaft yammie 80hp. The cavitation plate is not exactly spot on to the bottom of the transome but does the job. As you can see the other searider had a whole complete new transom as the old had hidden demons and completely rotten