F150/Bronco went through a major body style change in '87. Many F150's had dual tanks....... Don't think Bronco ever had dual tanks?
I would go to online sites such as:
Look up the same parts for both '91 and '83 and see if the part numbers, dimensions or whatever info they give, match.
Also you can look at web sites for auto-parts stores such as Napa, Autozone etc.