At WillowSprings, I come down the front straight at about 135mph, and brake hard for Turn 1. I'm almost standing on the brake pedal, and the front end is diving hard. The rear end comes up, and the car feels a bit squirmy, but even at that point, the ABS hasn't kicked in yet. So it would seem that you don't need ABS, if you threshold brake.
But as has been said above, my 01 car has different (Larger) rear piston size, gives it more rear bias. From that perspective, I'd say a pre-01 car might not brake just like mine does. I have to admit I've never braked hard in a non-ABS Viper. So the answer is either get an ABS car, or get new rear calipers for your pre-01 car. From Tom, I think! Thats the lowest cost fix. Then there are always the upgrades from Stop Tech, etc, if you wanna spend some money. The "front only" Stop Tech kit just reduces the front bias, and in that way, balances the front and rear bias, but sacrifices stopping force to do it. I'm not sure, but I think the 4-wheel Stop Tech kit has all-new piston diameters, that doesn't sacrifice stopping power to achieve front-to-rear balance. I could be wrong, better to ask Stop Tech yourself.
Its not likely that any Gen2 Viper could lock up the wheels at 150mph, there just isn't that much stopping force available.