I have twin 454s with thru hull exhuast and TRS setup using 3" spacer blocks. I am looking for a reasonable solution to upgrade the exhaust. My manifolds are new but I want a tube style riser that has the height I need to eliminate the 3" spacers. I would take a complete manifold/riser setup if it was reasonable. Must be in good shape, the whole point of this is to increase reliability. IMCO riser +3" would be ideal, need 2 pair. Also open to 496 retrofit but not sure I can get the height I need.