Do you have the "Old Merc" rams available to measure?
If so, measure them.
Then calculate the IMCO setup utizing the DELTA shaped center ram mount that has the hydraulic thru hulls at the apex of the delta. Figure the length of the IMCO rams required to make that work.
Then you can figure out utilizing independent ram mount brackets that are not connected together like the "delta" mounting plate. You will measure for 3 days trying to get it figured out and essentially will come up with rams the same length within an inch no matter what system you end up with. Remember, you have 34" between drives center to center. So you only have so much room to work with. If your rams are too long, you reduce your travel by not being able to shorten the stroke. If your rams are too short you will not be able to extend the ram far enough. The difference is going to be an inch either way. The available rams are not that exact.
From my experience....
Once you put full hydraulic on the boat you will almost never turn the wheel to the extreme of its travel anyway.

Thanks OPIE272 for that info. I expect to pick up the Old Merc rams in two weeks and will take measurements like you said.
Scott Smith of Formula emailed me back but was unable to give me the gimbal to bracket measurements that I was looking for.
I am going to try Mercury Marine when I can some info on a good Tech person there to contact. I have asked Scott Smith if he could supply me with a name and numer.
Appreciate everyone's help and I am sure we will eventually get things figured out like you mentioned OPIE272