318 4bbl upgrade. Help

That SP2P manifold has really small runners so an excellent match to your engine. I ran that same manifold on my 70 Duster 318 back in the 80's with a 600 Holley, fresh valve job, and mild Comp 252 cam. The car had a 904 trans w/2.76 rear gearing. Was an excellent daily driver. Driving from San Antonio TX to Joplin Missouri I averaged 23MPG.