Big Block exhaust manifold question?

[myyamr7]

I have a set of exhaust manifolds that came with a complete 402 engine I purchased a month ago and assumed they were out of a 72 C20, which is what the engine came out of.
So far, to identify the parts from this engine, I've used this chart which seemed accurate for the engine block and heads.
When I plug in the exhaust manifold numbers, I get 2 Left manifolds from a 73-76 what looks to be a police vehicle? The numbers off the manifolds are RH 353030 and LH 3994045.
I really don't care if the numbers match to a C10 manifold or not, more so are the exhaust outlets in the same location on these manifolds, vs whatever came original on a 72 c10? Reason I want to make sure, I'm swapping from a small block to a big block in my truck and I've found a company that makes the correct exhaust down pipes for the manifolds to hook to my current exhaust. I'd like to buy them ahead of time, so when I install the engine, I can break it in and go.

Thanks