Where to start?

Welcome guys! Nice Barracuda Oldfish! Lots of good 273 info here.Look in Forums or use Search. A 273-4 barrel can run good and you already have a fresh engine. If the engine is original to the car you will need a HP273 manifold for a 65 as the bolt holes are at a different angle and the bolts are smaller diameter than the 66 and newer manifolds. Those manifolds are still around but you need to be patient. My 66 Dart has a HP273 that I rebuilt last winter. It runs good but I only have a couple thousand miles on it and I'm slowly working out the bugs and tuning. Good luck