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
 

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.