I can't tell you for sure cause I've never looked on a 65 but my 66 was originally a unibody. I think yours is too. Look underneath, right by drivers door. If frame stops by tranny then goes to floor and starts frame in back again then it is unibody. You can connect the front and rear frame rails with some 2x2 iron to make it stiffer.
__________________  Darin
1966 Ford Fairlane GTA drag car 514
best et 9.26 @144
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