I think there is a little bit of over-thinking here. The box is only ever going to support it's own weight. It's unlikely to need the pins replaced and they could easily be cut off and new ones welded on, instead of being through-bolted.
Electrical diagnostics are a full time job but, I'd check all of the primary connections and the key switch. Get a multimeter so you can check voltage and resistances. Some professional assistance might be a good investment.
I bought a "universal" seat for my MF and while some of dozen the bolt holes were usable, I was seated way too low and forward to operate the tractor, even with with seat adjusted all the way up and back. I ended up having to fabricate a bracket for the seat. I think I paid $125 for the seat...
I haven't read all of the numerous responses, so pardon me if I'm repeating anything. Asphalt is a petroleum product, so your trying to remove oil from oil. It can't be done. You can treat the the affected areas with a primer and use a coal tar driveway sealer to resurface the entire driveway...
Hmm, seeing as it's for a B series, it probably won't be sufficient for my M. I'd like one that cranks up and down like my MF. Maybe I should just buy the MF part and modify it to fit.