Just a guess but I expect a Fuji from that period would require a 1" threaded JIS size headset and a 1" quill stem. I have no idea what stem length you require and you'll have to decide. Your current stem may have the extension length engraved at the bottom of the quill below the "minimum insertion" mark. Also, I also don't know what handlebar clamp diameter you need but I expect it's 25.4 mm.

Frankly, given the sizing uncertanty and the relatively low cost of these parts, I recommend taking the bike to an LBS and buying them there. They may even install the headset at little or no charge if you purchase it from them.