Doug - the emission sticker under the hood should say 'non catalyst' on it - and unless it was a very late '78 that was '79-spec, it should be cat-free. Ignore the 'unleaded fuel only' sticker - that doesn't indicate the presence of a cat. I'm pretty sure you have a pure '78 model year truck.
Colo Springs, CO
'78 FJ40, '89 FJ62, '98 4Runner