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IF it's a '65, it would be a 240 or 300. Intake and exhaust is on the passenger side on those. The prior generation had the intake and exhaust on the driver side.
As to how to tell if it's a 240 or 300, you can use a piece of wire down a spark plug hole, and rotate the engine. Note how far the wire moves. 3.18" = 240, 3.98" = 300.
Since it's apparent that the warranty plate attached to your driver's door is not the correct one for your truck, it would possibly be useful to find out what your truck's correct VIN is. Assuming you have a title for it, is there a VIN listed on the title? The VIN is stamped on top of your frame rail on both the driver's side and on the passenger's side. Annoyingly, the one on the passenger side is usually under the cab so can't be seen without removing the cab, but the one on the driver side should be found on the TOP of the rail, and I hope to attach a picture to help you find it. Sometimes the stamping isn't very deep so be very careful with your wire brush, paint stipper, etc.that you don't erase it while you are searching for it. If the VIN is correct, it might start out something like F10YK.... The F10 = F100 half ton two wheel drive pick-up. The next letter = which engine it left the assembly plant with depending on what model year it is (1965: D = 352 c.i. FE V8, 2 bbl. 1966 - 67: Y = 352 c.i. FE V8, 2 bbl. 1966: A = 240 c.i. I-6, 1 bbl. 1966: B = 300 c.i. I-6, 1 bbl. etc.) The next letter = which plant assembled the truck. K = Kansas City. There are about 10 other possibilities. When you find your VIN report what it is and someone will finish decoding it for you. Good luck! You might just be able to make out the VIN on the closest frame rail. The VIN will have little stars at the beginning and at the end.
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.