expert help needed (my first post)

Welcome to FABO @TheCudaKid ! Like most, if not all of the others that have replied, I'll suggest sticking with the small block. I live in Western NC, and I'm gonna make a guess that you live around Raleigh, maybe. There are several good machine shops down that way. Has your 273 been bored, or is it still the stock bore? Clean the top of a piston and see if you can find a piston size. Stock won't have one, and most oversized will have whatever size they are stamped into the top, like .020, .030, .040, etc. Get the machine work done and build it yourself. It's a great learning experience that is a major confidence booster. In 1975, I was your age saving every penny I could scrounge to build a 340 to swap into my 70 Duster that had a 318. I built that 340 myself, with some coaching from my neighbor. Much to my amazement (even now!) it ran, and ran like a scalded dog! You can do the math from my age above, in 1975, but here I am today at 66 years old and still love fooling with my cars. I do my best not to be one of the grumpy old guys, like @Dana67Dart mentioned....lol. Good luck to you, and keep your work updated here. :)