How hard is it to install adjustable clutch quadrent?

PITA indeed. Remove the driver seat (4 bolts I believe). Just be careful of the bolts sticking up when you lay on your back to get up under the dash.

It is worth the trouble though in my opinion - firmer feel since stock piece is PLASTIC!
 
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.

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.
 
Just did this yesterday

I installed a Steeda double hook quadrant and firewall adjuster. I used my OEM cable since it is said to be the best. I didn't remove my seat and I am six foot tall. I don't know what the neighbors were thinking if they saw me. It was pretty easy. EXCEPT for taking the old plastic quadrant off. I don't know how they got it one. The big piece is easy, it just slides off. The little piece is the pain.

There is a spring that goes through the long skinny part and around the back of it. I tore this off with some plyers. Take the clutch cable off through the firewall. The hole is big enough to see the spring and how it is attached. You could probably yank it off through the hole to. Once I got the spring off, I tried sliding the rest off but there is no room. It seemed like maybe my linkage was bent reducing clearance or something. I attempted to loosen the clutch pedal in an earnest attempt to gain extra clearance which did not work so don't waste time trying. I had to break the quadrant to get it off.

I broke the skinny piece that the spring went through and this enabled the piece to spin freely on its shaft. Push the clutch cable down as far as it will go and spin the piece until you get maximum clearance and slide it over. It will come off. You have to be mean to it and cuss it out but it will come off.

The rest was easy. In principle, this should only take twenty minutes but it took me about an hour and a half. Anyway, hope this helps and yes, the new set up feels a whole lot better.
 
I just did mine, the big peice of the quadrant came off easy but the little piece would not. I put a wieght on the clutch pedel and then pried it off through the hole inb the firewall.

93 5.8 GT