Vorshlag's stocks the correct custom U-joint from our BMW E36 Competition Steering Shaft Assembly to make your own steering shaft, if that is in your skillset. These were made for us by Flaming River to our specs to fit the 17mm x 54 spline BMW steering column and rack back in 2007 and we have sold many hundreds since.
One end of each model below has this BMW spline on one end and a 3/4" or 1" "Double D" on the other. This is for use with the industry standard DD shaft profiles. You can buy this shaft in both a 3/4" and 1" DD sizes. On our E30, E36, E46, Z3 and collapsible steering shaft assemblies we use both sizes - the 3/4" DD shaft fits inside a hollow 1" DD shaft - to allow the steering column to collapse in on itself in a front end crash.
These U-joints can be used to connect a BMW steering rack or column, and works with E30, E36 and E46 BMW steering racks. This is a bolt-on steering U-joint is CNC machined from ChromeMoly Steel, and makes for a low profile needle bearing U-joint to allow precise steering inputs without the factory "Rag Joint". This is "made for off-road use". Each joint includes 3 set screws and jam nuts to lock onto the splined end.