Help please, E30 coilover/suspension question!

You probably need to measure the distance between the holes on the struts

Prab

do the bauer cabrios have the same suspension as regular cabrios though?

Generally, 4 pot cars have the smaller strut diameter, 6 pot cars the larger diameter.
There is a better/cheaper/lower way if you're handy with the fabricationings and have a pair of the 51mm struts.....
Right, a lad I work with just got into E30s after an upbringing on VWs and was disappointed at the lack of cheap lows for the BMW.
So, Compact has cheap ebay coilies available, Compact rear is the same as E30, albeit slightly higher, so the rears from the kit are a straight fit, they drop it more than lowering springs and give you a set of short dampers should you need to remove the adjustable platforms and find some shorter pigtail springs (Corsa B?)
Fronts, The E30 front legs have the hub carrier integral so dismantle the coilovers, remove the inserts, with the thread removed from the lower adjustable section they fit inside the 51mm struts. The inserts they come with are shorter than the stock ones so with a bit of measuring you can weld the top part of the coilovers into the bottoms of the 51mm struts and then replace the inserts and build them back up. This will allow you to go very low for not much outlay. His E30 will lay the sump on the floor! The front springs are very stiff though, the compact must be heavier than the E30. Springs are available from Rally Designs or Demon tweaks though in lower poundage and he's working on this at the moment to get a bit softer ride on the front. I'll try and get some pictures off him tomorrow to try and explain the fronts a little better.

Pretty sure the set-up BiAS is describing involved shortening the struts. It sounds like he's talking about using the lower half of an e30 51mm strut with the top half of an e36 compact strut welded to it at the right length for the e36 insert, which sounds like it's shorter than the e30 one. Sounds like a good set-up, softer springs may work well with the dampers too, as most people seem to find cheep coilovers a little over spring and under-damped with the springs that come with them, softer ones may well work nicely.