Hi guys,

I have a 86 vette with 275/40/17 Kumos that are toast up front. I have all new suspension with crappy Gabriels in the front and Monroe's in the rear.

How can I get a smoother ride? Can I run 235/40/17 all around that are rated at 50000miles?

I don't think a 50,000 mile tire will stick to the road very good.
I love my bilstein shocks nice firm ride

How can I get a smoother ride?

Define smoother?
The ride is determined by the springs; shocks only control the bounce.
Tires affect ride but a 235 will be stretched tight on a 9 1/2" rim intended for a 275 so it will ride harder.
The smallest tire the factory put on a 17" rim was a 255 on a 8 1/2" rim which is narrower than yours