What a splendid notion!
I'm thinking hydraulics with steam providing motive power. You could mechanically adjust gun alignment for beds hydraulically coupled to a sight and trigger command station. Ideally there would be a way to remotely couple "trim controls" from the command station to the adjustment system for a given gun.
Some smaller guns could fire tracer rounds for walking your range to the target, with a very steampunk GBL to (dis)engage the loading/firing systems for the big guns.
An interest of mine is bootstrapping, which is the planned reconstruction of high technology industrial pyramid. You can't just build a silicon wafer factory, you have to iterate through levels of tech in a cycle of building both the tools to build the tools and the necessary industrial capacity to grind up a mountain for a kilogram of iridium.
Part of the problem is warlords with remnant tech. Even if you grab lots of stuff in the fall, sooner or later you run out of ammo and parts for your fancy toys and you need the sort of thing described in this question to hold others at bay while you Take Over The World™ in the process of securing the surprisingly large resource base you need in order to reclaim the stars.
Low tech solutions like this have the wonderful quality that you can surprise deploy them. Use the ranging guns to feign firepower till they're in ideal range, then EMP your enemy back to the steam age with a very special shell. The rest of the battle should be rather one sided (or maybe you want their ships).