buy the heads first. the corvette engines from the late 80s were lame on a good day,ask me.
the heads will determine the entire build.That flat tappet cam is not going to get you to 400 hp
my 81 350 with manifold,modified 650 holley,actually flowing 780 cfm,1 5/8 headers,small comp cam.stock heads made 205 hp at the wheels.
Ive fixed that problem