Replacing it with a newer unit shouldn't be a problem.

There are many on the bag. Most new ones are boxes and may be easier to hide.

http://motors.shop.ebay.com/i.html?_nkw=charcoal+canister

Some newer canisters are nearly identical to Mopar canisters of the day which leads me to believe they were probably made by the same company.

GM http://www.ebay.com/itm/270946231006
Nissan http://www.ebay.com/itm/180855366667
Jeep www.ebay.com/itm/130673142627
Old Mopar www.ebay.com/itm/150631341834

All the canisters should be labeled (Purge) (Vent) etc. IT shouldn't be too much of a problem to plum a new one in place of an old one and just cap the unused ports. My 73 uses the same can as my 74 but my 74 has no bowl vent so the port had a cap from the factory.