Question on new transom core material

[Capecafe]

I'm restoring a 1978 MA and need to replace the transom. I am planning to replace and raise the transom from the outside and have a few questions for all the experienced boat rebuilders:

1. I have 1.5" of core material to replace. Since I am replacing from the outside I'll need to cut my replacement core into pieces in order to fit tightly back into the edges. Would a single core of 1.5" Penske board, cut into 4 pieces then sandwiched between two sheets of 18oz biaxial cloth with the original .25" outside skin epoxied on be sufficiently strong? A few of the outside transom replacement threads have used two layers of core with overlapping seams. I am repowering with a new 2016 Etech 150 that weighs 420lbs.

2. I have been told to be careful when raising the transom on the MA to 25" in order to avoid an issue with the motor mounting holes. It was mentioned to either go 26" or 24" to avoid a problem with the lower mounting bolts. Is this a real concern you all have worked around? It seems the new Etech has plenty of mounting bolt locations to work around this issue.

3. When determining my transom height, should I measure from the bottom of the keel up to the top along the transom, or top of the transom straight down to level of the keel?

I've attached a few pics of the boat when I found it and before I started the restoration. It was a freshwater boat it's whole life, but the through hulls in the splash well leaked and turned the inside of the transom to mulch. The foredeck and alongside the console were mushy and I've already re cored them as well as the fuel tank cover. I had a new 42 gal fuel tank built and have installed that with all new hoses. Plan on keeping the boat, so it's important I do it right the first time. I appreciate any thoughts you all have to help me make sure I get it done and done right. Thanks!