Purchasing a full length header for my 1972 Cutlass STOCK bottom end Olds 350. Any recommendations on which primary and collector size to use?

1 5/8 primary X 2 1/2 collector OR
1 3/4 primary X 3" collector

Using E Performer with Holley 750 3310.

 

I'd use the 1 3/4.

 

x2

 

I might have a set here for sale pretty soon. still in good shape. 1 3/4 primary.

 

I say 1 5/8" but either will be a massive improvement.