I am in the process of doing a stock floor, firewall back frame rebuild with a 302 swap at the same time. The whole truck is torn apart right now and I am trying to figure out the measurments to build the new frame.

I would like to run a 265 tire on the rear and I am not sure if the frame will clear at stock width or if I will have to narrow the frame. Does anyone know? I am going to be running an 8.8 with disk brakes and im aware that I will probably have to have the rear end narrowed. but will the tires fit between the outside of the fleetside bed and the frame or will the frame have to be narrowed?

Any help would be appreciated.

Depending on wheel width/offset, yes, the tire will fit with no problems. Mine are 265/35/18, and they look tiny. Much larger tire could fit. However, mine is a 10" rim, (which measures 11" from edge to edge). The rim itself is about 1/4" narrower than the the stock wheel-well opening. With a 9" wheel, your tire and explorer rear would have no fit problems, without narrowing the rearend (or the frame)

My fleetside has a narrowed 8.8 with 275/40/20's and have LOADS of room tween the bedside and frame.