TOPIC: Transom thickness

I am putting a new transom in my Thompson, and I was wondering if someone could save me the work of pulling my 1977 Merc 115 off the rack to measure and tell me how thick I can leave the transom? I have 2 layers of 5/4 lumber measuring a full 2 1/2 inches plus I was planning an aluminum plate on each side. If anyone has a motor or even a clamp laying around that they could get a measurement I would appreciate it.
The old transom is only about 2 inches thick. If I need to I can use a router and take a little off in the area of the clamp on the inside to make it right. I would rather leave it as thick as I can for obvious reasons.
Thanks,
Bill