Engine should be ok. Hopefully tank had gas in it that diluted some of the oil.
First, don'the run the engine, then drain the fuel tank, change fuel filter and clean out the fuel lines. Can diy with Eastwood Aerosol Injected Cleaner item #12846Z. Gas tank cleaner is $$$, can you do it yourself?
Local station had a tank of diesel put into its storage tank just before we filled our son's car; same as with you, it would crank, but not run. We had the car towed to a Ford dealer to empty the tank and clean it and the lines, new filter, and injectors were flushed. Station paid the $500.00 bill, but would not reimburse for the 9 gallons.
Oohhhh thats weird. 1990 is my favorite Bronco model. At least it had something so I hope your engine is not fried. I would suggest the same as miesk5. Get everything flushed out, then pour some new engine oil and see if what happens. I wish you found out about it before the Bronco stopped. I use to work as a lube monkey and forget to put oil in an engine. That car got fried and the company paid $3000 grand for it. For some weird reason they didn't fire me.