Is this an acceptable grounding layout

I have my PDM in the glove box and a pair of firewall power posts behind the dash, my initial plan was rather than running a ground cable from my PDM through the firewall in the main harness to instead just ground my PDM, ECU and CANBUS to a ground post in the glove box where they all live and then run that directly to the ground post on the firewall. Stuff like injectors and ignition coils will be grounded to the head, thermofans to the chassis and chassis to the block.

What you're proposing will work BUT it can open you up to the potential for issues. The problem is that if the ground cable to the engine block from the chassis is left off by accident, or is damaged for some reason then you could run into trouble which is why we recommend the star point earthing strategy with the star point on the engine block. It's up to you ultimately how you choose to progress and the reality is that it'll probably be just fine but there is the potential for an issue.

Just another note on the injectors and ignition coils - The coils will require an earth and that should be to the head typically (we want this to be as short as possible to avoid the potential for ground loops), however the injectors are supplied power (from your PDM), and then the earth is switched via the injector drive in the ECU. I trust that makes sense?