The aftermarket quadrant can be installed without major disassembly.
Here's my experience with the FMS quadrant kit...
The under the car part was easy- getting the old quadrant off and the new one on was my problem. Look closely at the amount of clearance between the pivot shaft for the quadrant and the metal bracket to the right of it. You will need about 1" of clearance to slide the old quadrant off the shaft. Then take the ratchet mechanism off after that, if it didn't come off when you removed the quadrant. It may be inexperience on my part, but I had less than optimal clearance. I had to destroy the ratchet mechanism by drilling a pair of 1/8" holes like this - oo, the two 'o's are the holes drilled in the ratchet pawl parallel with the shaft. The holes are drilled in the part of the ratchet that pivots on the shaft. Then place a chisel inline with the holes to split open the ratchet pawl to get it off the quadrant .
The shaft for the quadrant pivot and the pin in the end of the clutch pedal MUST be perfectly parallel for the FMS quadrant to fit the first try – mine wasn’t and I had to enlarge the hole for the clutch pedal pin to get it to fit. Once you get to the cable, you will notice that the firewall end has an ear on it with a small hole in the ear. I recommend that you seat the cable against the firewall, line the ear up so that you can drill a hole in the firewall and use a sheet metal screw to secure the ear to the firewall. This will hold the cable in place while you adjust the cable. The rest is fairly easy. When you take out the front seat, put a large piece of plywood or a metal plate over the seat mount studs so that you don't tear up your back while scooting around under the dash.