"...premier resonator bass drum tom mount is cracked, and needs replacing. Anyone know how to access the inner fixings to undo them and get it out??"
Yes...but it is a very delicate operation.
Each drum has a round thin veneer inserted between the outer shell and the flat inner edges of the top and bottom reinforcement rings to produce the "resonator chamber", which is in fact an inner compartment of air which resonates.
The thin veneer inner ply is held perfectly in place by its opposite ends meeting each other and generating just enough resistance so that the inner ply "snaps" into place, forming a perfectly circular inner wall!
To access the internal nuts and washers which attach the castings:
1)Remove top and bottom heads and visually identify the "seam" inside the drum's inner shell where the two opposite ends of the inner wooden ply meet.
2) With an extremely thin but strong tool (like a butter knife), gently and with extreme caution wedge the blade tool into the seam to separate the joint.
3) The inner ply will then "pop" loose - this extremely delicate one ply veneer of wood must then be carefully removed and set aside in a safe place where it can not be stepped on or damaged.
4) The internal fasteners are then readily accessible for you to remove and make repairs.
To reinsert the inner ply you simply reverse the above process:
5) Manually reinsert the circular ply into each drum, carefully maneuvering it back into place, until a perfect circle is formed and the two opposite ends meet and slightly overlap.
6) Using the edged blade tool delicately pry the two ends apart until the ply "snaps" all by itself back into its former shape and position forming a virtually "seamless" inner ply shell wall.
Now you know why the line was discontinued - in spite of it being one of the best sounding kits ever made.
Good luck!