On Sun, 11 Apr 2004 20:58:51 -0400, John H
wrote:

Remove the exhaust manifolds and risers.

==========================================

That's the right place to start.

I just went through a similar issue with a 350 and it turned out to be
a badly rusted cylinder head. Ended up replacing both manifolds and
risers, both cylinder heads (and valves), the thermostat housing, the
distributor, and the harmonic balancer.

Expensive toys, these boats.

In retrospect I wish I'd sprung for whole a new engine.