when I converted mine, I mounted the 4-spd to the bell housing with the shifter installed (with out the shift lever). Then from underneath I marked where the opening would have to be. I removed the tranny, drilled the corners of the marked opening and cut it out from the top. Worked well. I did have to enlarge it a little after final assembly. For ease of installation I did not have the clutch installed the first time I set the tranny in. Good luck and enjoy that 4-speed.