Not sure what you are specifically looking for in terms of advice. Seastar is obviously the best of choices. I upgraded my 2005 208 years ago to Seastar hydraulic after the original steering froze up on me and it was a significant improvement in steering. The one thing that i do recall is that the old mechanical steering could no be removed 'cleanly' without the engine coming off - the cylinder of the assembly was too long to come out. Instead of going through that ordeal (it would have been an ordeal at the time) of hoisting the engine off, we popped an inch and quarter (or so) hole on the stbd side wall of the motor well, which gave the cylinder enough room to come out. I can't tell you that you will have the same issue, i'm just conveying what I remember of my challenges.
given you are switching to hydraulic, you can solve the issue quickly by cutting off the old steering cable which trashes the old cable (which intact is worth about $50 used). if you cut it, best to loosen it first to freely move in the motor tube if you can while still connected to steering wheel before you cut.
it is pretty standard that a conventional steering cable will not have enough room to come off (or go on) an engine in a splashwell unless you unbolt and lift/move the engine along the hull away from the cable. you can check cleartance with a tape measure keeping mind that if the access hole in the splashwell is offset even a little from the engine tube you are likely hooped even if there appears to be enough room).
As the cable comes out and approaches the side of the splashwell. couldn't you just cut it off near the engine bracket with a cut-off wheel on a grinder and keep sliding it out and cutting off pieces till it was completely out. I'm not sure I am picturing things exactly right so if that sounds stupid then I probably am.