I would be surprised if it's not a dual bolt pattern bellhousing - that's why they made them, so that they didn't have to make separate bellhousings for 3 speeds and 4 speeds. If you take the 3 speed transmission out (leaving the bellhousing in) and there are 8 mounting holes, you're good. You then should be able to just put the 4 speed in, with a 4 speed shifter and shift rods, and have your driveshaft shortened to the right length. I believe the transmission yoke is different for the 3 speeds and 4 speeds also, so that will most likely need to be changed. You will also need to get 4 speed E body transmission levers. The shifter mounting bracket may be the same between the 3 speeds and 4 speeds, but I’m not sure. The shift rods from the 3 speed may be able to be used as the 1-2 and 3-4 rods on the 4 speed, but I’m not sure on that either. If they do, you would only have to get a reverse rod for the 4 speed. The best thing to do would be to test assemble the transmission, shifter, shifter bracket, levers and rods outside of the car first, and adjust the rods at that time – it’s much easier to adjust them outside the car than in the car. Then make sure the adjusters don’t spin when you disassemble it and install it in the car. The clutch, clutch linkage, Z bar, etc won't need to be changed, or even removed while you make the swap, but if the clutch, throwout bearing, and pilot bushing are old and getting worn out, you may want to replace them while you’ve got it apart.