Here are the bits needed for a larger starter.
Battery: (used in the MX-5)
http://www.atbatt.com/interstate-meg...ry-370-cca.asp
Tray:
http://www.northernautoparts.com/part/de-00252
Post clamp: see pics...available everywhere in multiple versions.
Remove (unscrew) one of the hold down block wings, cover sheet needs to be cut/trimmed for Neg post terminal.
This set-up was tested for a couple months last winter.
Rob.