Minor amount of coolant on passenger floorboards ('68 cuda, '94 360 mag)

Finally drove my Cuda to work today, and on the way home noticed a bit (like a tablespoon) of coolant dotting the passenger floorboards. Inspected the heater housing, couldn't find source. Heater core is fairly new reman, after the last one went (with the typical massive fogging, dumping coolant symptoms).

My temp gauge stays rock steady at 195F. It's been sitting for a while (in garage). Any ideas? Just a burp/hiccup?

I'm a nervous nelly, would hate to overheat in traffic while commuting!