magnum valves are too big for a stock 273 without notching the bore....

I'd probably limit it to a dual exhaust system, intake and 4bbl, parts that can be easily swapped to a larger engine. anything more than that, you're better off starting off with a 318 or 360...

1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)