I need to know which aftermarket suspension system is going to make it handle as well, and feel as smooth, as possible, as close to a modern car as possible.
Hotchkis and Firm Feel can do this with the stock system for around $3500. Add in a Borgeson steering box for $1400 and you are there for under 5 grand.
As far as AlterKation vs XV;
AlterK is Mustang 2 based, XV is Corvette based.
AlterK is all mild steel, XV has some pieces made of cast and extruded aluminum.
AlterK front is a direct bolt in, rear requires minor welding. XV requires cutting and welding on both ends.
AlterK will cost around $10k for front, rear, and brakes. XV will cost around $10k front and rear once it is optioned out and equipped with brakes.
AlterK comes with adjustable shocks you will need to dial in, XV comes with pre-valved, combination specific valving that you bolt on and go.
AlterK will offer one free spring exchange while you are setting up your system, XV comes with pre-determined spring rates.
Alterk has a reputation for exception service and support. XV was bought out by a former employee and is improving customer service and support.
AlterK has sold thousands of systems for performance street and drag racing applications. Xv has sold hundreds of kits for performance street use.
Both are coil over, R&P systems that allow quick spring changes, easy ride height adjustment, steering precision, combined with compact size and light weight.