VP, VR ish Commos have a nice, modular set of relay holders. Might be easy to modify. I also heard recent Falcons have something similar.
However I think most fuseboxes will be a pain to make fit since you'd have to sit down and work out which input wire went to which fuse and relay. It would probably be easier to make a full custom setup. A few relay bases and fusebox screwed to an alloy plate would do the job.
Hen