If your 6 banger is a 230 or 250 a small or big block v8 will bolt in with virtually no modifications. You'll only need to find the proper engine mounts to attach to the frame brackets. The frame brackets will stay in the same position they are in with the small 6.

If you have the big 6 (i.e. 292) then you'll have to change the passenger side frame bracket mount. Find one from any 63-72 truck with either a 230,250 or small block v8.

Even with the big block v8 you'll find that you'll still have plenty of room to work under the hood.

-ftyler