Quick question about BFG Radial T/A's

he told me the 205/70R14 will fit on the wheels

They will fit (i.e., you can mount them) on the 4½"-wide wheels. Doing so, however, is a poor idea. "Ten pounds of poop in a five-pound bag". It's really not a good match, and even Goodyear's own literature on that tire says the appropriate rim width is 5½" to 7".

How can I tell if the wheels are 5 1/2"??

It's easy to tell the narrow from the wide wheel if you have them next to each other, or if you've seen enough of them to be able to spot the difference from the outside. If not, dismount the tire and you'll find the rim width stamped on the wheel barrel: "4.5JJ" or "5.5JJ" (letters may vary).