Will these stock ex manifolds seal off without heat riser?

[72farmer]

I have a 72 c-10 w/ a small block that I am trying to finish up. I am going to take my headers off and install stock manifolds.I am then going to take my truck to the exhaust shop to get new exhaust pipes ran all the way out back.I only have 1 of the heat riser valves.Can I remove the valves and get 6 shorter exhaust flange studs and do away with the valves?When I remove the valves there is a flat surface and not chamfered for the donut gasket to seal on.Will this work or do I need the risers to get the donut gasket to seal?Also are these the correct ex manifolds for my 72?