If those use the Mallory caps and you want to replace them in kind, CDE has picked up the line which is now the CGS series. Mouser has a 39,000uF in stock. These are tough to find without having to place a factory order (which is a minimum of 24 to 36 pieces and can costs thousands of dollars).
Nichicons have metric threads and may be a problem if other things screw into the caps. Kemet caps are cheaper, but they are fairly new and don't have a long track record and could cause problem later (as Mark Levinson 300 series owners found out the hard way with the Philips caps).
You can go smaller in diameter, but not bigger (or else the ground bar would have to be re-drilled). As long as the bottom plate is clean, it isn't too big of a job to put in a smaller clamp. Aslo, check how much play you have up and down -- or you may be stuck without a length option.