You dont mention what machine you are using or if the present set up is achieving the production rate.Is the surface finish affected with this set up
If by removing this platform you can improve the production rate then your production department should listen to you .
Unfortunately at some...
Cant see much wrong with the process for the seat insertion, but if the seats are not holding with the clearances you have given plus loctite I would consider electron beam or laser welding and compatible materials for valve seat and valve ie stellite, had this same problem with loose seats on...
Also not able to open your attachment, sounds like you need location dowels fitted to your frame prior to bolting down the plate .This would solve any misalignment , but you would of course need accurate alignment prior to drilling the frame for the dowels.
Not a good situation .Very like a person applying for a new job and getting a bad unjust reference from a former employer,(and you dont know about it) which happens a lot.
Prefer to work with Delrin and for both you will need very sharp drills, milling cutters etc have you considered Tufnol a superb material to machine Tufnol.com