Not an expert but I think if you want close to stock tire height It's 235/75r15 LT (nominal height of 30"). At least that's what I have found out about my '79 F150. Yours might be different especially if you have narrower rims. You don't say if it is 4wd or not.
Mine is 4wd with stock suspension and currently has 33x12.5r15 LT's on it but I'm thinking I might go back down.