Your 78 300d or 84TD will roll very nice on a set of Defenders or any of the other Michelin tire models, Primacys, MXV's, etc. The Defender is Michelin's new tire and it replaces one of their older models........I'll have to dig thru my notes to recall which one. You're on the right track. Where have you been looking, tire stores, Craigslist, eBay?