Nice looking Explorer!
I have a similar situation with my stock '75 Sport with no rust and 65k miles when I purchased it. I say none but acutally there was some surface rust on the floorpans but nothing to really worry about. I also believe that the hard top had never been off as the bolts and seals were in perfect condition.
I struggled briefly with replacing exhaust, brakes, etc... due to everything being original but after several weeks of owning it I quickly realized I bought it to drive and enjoy not to pamper it and one day put in a museum.
I still struggle with decisions to modify but have so far installed a new brake master cylinger/bracket/booster from Tom's and am so glad I did. What a difference especially with drums on all 4 corners. I also put on long tube headers and dual exhaust and being it's a '75 and requires "cats" I like the fact it can breathe easier than with stock exhaust manifolds. I saved the orignal manifolds for any future owner but did throw the old exhaust pipes and master cylinder away as they were shot, leaking, rusted, lid dented, just worn out.
I have a roll bar and bikini top I have yet to install and it comes down to not wanting to drill 16 holes in my truck to install it. But I want so bad to ride around this summer with some shade and better protection in case of rollover. I figure since I've owned it 2 years, have no intention of selling it, see where most other EB's have roll bars....that I'm going to go ahead and do it. If I ever do sell and lose a little money on it, oh well, it is the price I pay for having enjoyed it so.
I also need to update the headlights with a better system as I have to drive at night with my brights on. Not sure the best route to go on this yet but definitley needs improvement. One day I will install disk brakes up front as the drums have their limitations but the one thing I'll never do is cut the rear fenders! I have come to the conclusion I need 2 EB's, this one and another that is modified more for off road use....just wish I had the money for the second one.