I.O engine mount help

[bigeasy1]

I'm getting ready to do a transom replacement on my recently purchased 1974 Tsunami I.O,and have a few questions.
Asyou can see from the pictures,the short box stringers that the engine was mounted to,need to be rebuilt.The original mounts in the picture had a raised portion where the front engine mounts were fastened.
Should i make the new ones the same,or should i make them flat across the top for their whole length?.
The original engine was a 351 Ford,but i will be replacing it with a 5.7 350 GM.I figure that it might be better to make them flat across the top,and raise them if necessary when i get ready to install the new engine.
I'm also going to do the transom from the inside,i know that it's more work than from the outside,but i think it makes for a neater and more secure repair,and it doesn't compromise the integrity of the hull.
Any comments or help would be much appreciated.
The pictures in order are
(1)bilge area before cleaning
(2)bilge area after cleaning
(3)Raised motor mount area,showing the deterioted glass and substrate.
Should i make the new ones flat across the top,and are any measurements available for Mercruiser engine and outdrive placements,such as location of transom cutout in relation to engine height or placement
Thanks again guys.
John R.