Exhaust Manifold Application Question

Now thats pretty interesting....not a significant loss in power using the 318 manifolds over the 340 manifolds. Either way for now i'm going to run these manifolds...

Is there anything to be gained or is it necesarry using a 90 degree oil filter adapter with manifolds?
When I pulled the 273 out of the barracuda I noticed it had one but it had no exhaust so it may have had headers at one point.