I found a G.M. oil filter canister at a swap meet for $5.00. No bracket--but still good. I drilled two holes into the canister from the back--one above the other--and put 2 sealed bolts thru to mount it to the firewall. Then cut a grove in the upright to open up the tube on the bottom--now it's a coolant overflow bottle--coolant in from the bottom--overflow from the side. I hard-lined it to the radiator--everybody thinks it's an oil filter.
OK, that settles it! I've been trying to come up with an idea for a overflow bottle, this IS it! Good thing we have a swap coming up!