Is there a spec document for the compute modules, including detailed pin out descriptions, physical dimensions, etc.
All documentation for the Reform is linked from here: Documentation: MNT Reform—MNT Research GmbH
Pocket Reform: Documentation: Pocket Reform—MNT Research GmbH
What you are looking for should be in the CPU Module Electronics Sources, linked from the main Reform docs. Electronics sources are in KiCAD format. There are 3D models in STEP format if you need those for dimensions. There might be simplified PDF design doc exports of the above, not sure where though.