Linuxcnc Cylinder Head Valve seat cutting machine

Hello guys,
due to the fact that i am repairing car engines, i would like to be able to do some work by myself instead of giving, e.g. the cylinder head to a machine shop. 
I thought to build a manual seat cutter, which is not pretty hard, but the problem is that i would need a lot of different tooling and cutting bits as well as learn to use them and that means a lot of money + time. Yesterday i saw a CNC Valve seat cutting machine, which technically seems not to be  difficult to build, but i believe no one here did that so there will be no post processor available and programming the cutting process is another thing. That machine has a "floating/flexible" spindle, so you set it up by putting a pilot shaft thats mounted to the spindle, into one of the valve bushings. Then you fix the spindle position. After that only 2 axis work. The Z axis and "X-Axis" that is mounted to the flexible spindle. The seat shape gets cutted by moving the cutting tool on that X-axis.
Here a link to the CNC Valve cutting machine - you can see the moving tool axis in the first seconds of the clip : 
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I got the idea to build such machine on yesterday late evening, so i didnt had really a lot of time to think about it, but maybe you can give me some tipps. 
Best regards, 
Denis
 

Interesting, XYZ like a regular mill and then U,W similar to an X,Z lathe setup.
In my eyes the challenge would be in the mechanics of the spindle head, since you would need to get U axis integrated into the rotating head.

Thanks.
Yes, the mechanical part is for sure not easy.
I am currently thinking if i can do it without cnc/steppers. Just mechanics.

Tree used to make a taper boring head which is kind of what your looking for in a mechanical solution. Robin Renzetti shows how to use it in this video:

Thats helpful and i was thinking about something like that, but a little bit different - it might be good, if possible to do, but for now i want to get back to cnc.
I might be wrong, but as for the post processer i could use a standard linuxcnc turning post processor and program it as i would do a lathe job.
In such CNC Facing Heads (e.g. U-Tronic Head) the W axis acts like the Z axis in a lathe, and the U acts like the X axis, so in this case i should be able to program the job same as i would cut a ID Taper on a lathe.