Porting will make much more difference on a dp engine. In essence you have twice the air flow area of the sp. Still only as good as the whole combo. Gasket and manifold matching, and de shrouding the valves/valve guides is the only thing that will do anything unroll you step up to bigger valves and bigger engine size, then porting really makes a difference.
Ratio rockers is like putting a bigger cam in without splitting the case.
So if I were doing these in some kind of order.
1 ratio rockers
2 heads refreshed, valve jobs, prt matching and light casting and deshrouding
3 1641 fresh pistons and cylinders (with the refreshed heads) and slightly more cc
4 then comes splitting the case to build something else, go with at least 1776, the 110 is a proven cam. And this will work with the dual singles or a 34 pict until you upgrade carbs ( I would go dual port when doing anything over a 1641