I have a 1987 E38 with exactly the setup you mention. There was an old Autohelm which was failing on the boat when I bought it. I kept the old linear drive unit (about 25 years old) and just replaced everything else.
Some older linear drives are not the same as others as I had the unfortunate experience to learn last year. Replacing the early generation Raymarine 6000 unit (dials only) made a (30 minutes on hold) call to Raymarine to see if my old ram would work. Explained exactly what I had "not the ST6000, the early 6000, two dials, no digital readout" and asked specifically about compatibility of the EV-200 with the old ram. The tech reassured me the the old ram would work "oh yeah, the design is the same going back to the beginning" so I dropped a bundle of $$cash$$ into the water to pony up for the below deck autopilot upgrade.
So when the unit arrived I spent a few hours practicing my below deck & small compartment yoga. Could not figure out how the EV wiring could possibly connect to the old linear drive. Called (25 minute hold time, they're getting better) Raymarine tech support again, explained (again) exactly what I was replacing and got the response "not compatible, you should have talked to me the first time" and before I could barely say "but, the other guy..." got hung-up on by the tech.
Hung-up upon. Excellent service Raymarine. (I did write up my excellent customer service experience and sent it into the tech supervisor via a very kind and sympathetic customer service operator. Still waiting for a call back a year and a half later. What's the likelihood the tech supervisor is the same [redacted-salty sailor like explanation of anatomically impossible events] that hung up on me?)
So I had to drop another $$grand$$ on a new linear ram drive. And turns out the [redacted, Nixon like expletives deleted] hang-up tech was correct. They changed the connecting wiring and moved the mounting bracket bolts about 1/2". Had to have a 1" extension welded onto the boat's mount, and then drill new bolt holes. Put in another 3/4's of a day of small compartment yoga, staring in close proximity at the peeling paint in my aft lazarette (reminder add painting the interior of the lazarette to to-do list), while braille fingering the mounting bolts into place and [redacted] [praying vigorously] installed and wired the new ram.
So now when you see me working on yet another project that has educational or religious benefit "oh god, not another life lesson" in the close proximity of youth or persons with delicate ears. I'll just shake my head and curse under my breath "Raymarine". The only cursed expletive that comes to mind to shake dried salt out of the sails but won't peel paint.
BTW, I still have the old 6000 (two dials, no digital readout) head and "early" type I linear ram scattered in various compartments if you need parts, pins, or mounts for repair. Probably not for much longer though, as rounding them up and sending them off for recycling has just been added to the to-do list.
