The pissing matches in this post are nuts. Bloke asked a simple question.

I've done all this to an M body in increments and can give you a fairly good cost/benefit breakdown.

Assuming you already have modern radial tires on the car, as suggested first thing to do is eliminate the ISO biscuits. Firm Feel sells the blocks you'll need to do this for the front end. You can probably skip over eliminating the rear, but I wouldn't. Convert it to an earlier B body solid shock plate setup. Get the front and rear bars from Firm Feel. The difference in handling at this point will be astronomical. Ride quality won't take that much of a hit.

From here you can decide if you want toss money at taking it further.

If your car doesn't have frame ties in it yet this would be the next thing to do. It'll make another huge improvement in handling and overall feel to the car.

Past this point you're looking at expensive shocks and different torsion bars and would warrant an entirely new conversation.

Good luck.