This is straight from Chevrolet Division.....
"Do not try to modify either the heads or the intake manifold to try to make the Vortec heads match up to a standard 12-bolt intake manifold. The ports will not match up. You must use a Vortec style intake manifold with any Vortec style cylinder head."

That tells me that the '87 TPI manifold will not work with the L31 heads.