A long time ago I bought a house, and almost immediately I put a simple 2-post rack in it to host some basic networking and home audio equipment. Then some stuff ensued, and I decided I wanted a server for my home. Well servers are big and heavy, come with rails and need a 4-post rack.
My lucky ass, just happened to of positioned my 2 post rack, about 34 inches away from an open framed wall. Given that standard rack depths are 31.5 inches I had something to work with.
First I had to modify my 2 post rack to actually accept the frame rails. For strength my rack post are in U shape and not standard 90-degree corners you see on a 4-post rack. So I had to cut away a portion of metal for the rails to fit into.
Once the posts were ready, I put the rails in, got a level and square out to make sure they were set to the right spot, and screwed them into strategically placed pieces of 2×4 wood on my open framed wall.
Finally put the server in, and crack open a beer.
The server slides in/out of the rack with ease, even a few months later. So I guess you can call me lucky for putting the 2-post rack where I did.