[Captainfab]

With the '63-'66 trucks the I6's (230 & 250's) and the V8's motor mounts are in the same location. The '67-'72's had different locations for the I6's and the small blocks. There are a few different headers that will work, but that depends somewhat on what trans you are running....manual or auto. Also if you are going very low with your suspension, regular long tubes won't be a good idea.

I usually prefer to use long tube headers for the '73-'87 trucks since they are closer to same length tubes than the ones specific to our trucks. Plus there is a better selection. Here are a few for you to look into that will fit the chassis. However if you have moved the engine forward, I couldn't guarantee the fit.

Hooker 2452's will work with a manual trans in the stock location.
Hedman 69090's will work with manual trans, but will possibly need to modify the bellcrank and rods some.
Hedman 69099's are for D-port heads. I think they'll work with a manual trans.
Hedman 69230's are for 4x4 applications. They are basically long tubes, but they don't hang below the frame.