I have a Simrad AP 25 on my GB (it is cable steering), I want to switch to a Raymarine EV series AP.
Is there any reason why I can't use my Simrad linear drive pump/ram with a Raymarine system?
I am not familiar with your ram (or which size EV you are going with), but one of the reasons I chose a Raymarine EV for my boat is that it could be used with "any" type 1, type 2, etc. pump. I didn't already have a pump but I wanted to use a specific (non-Raymarine) pump because it fit the tight space better. (The equivalent Garmin AP required their brand pump.) I have hydraulic steering though
I can recommend Raymarine's online technical help forum. It can take a day or so to get an answer, but they are a fount of information. Here is the Autopilot sub-forum:
It looks as though maybe you'd be choosing the EV-200? I can't get that manual to download for some reason right now (probably something on my end), but it's here if you have not seen it:
What is the issue with the Simrad integration to Coastal Explorer?
I've found Simrad support to be very helpful. That said, I have also found the Simrad EVO software to be very difficult to work with, poor documentation and it seems to lose/change configs on it's own which is very frustrating.