I believe a 1974 250 is non-integrated.
I checked Langdon's site and the split header is out of stock. Surprising! Give him a call, though, as that's what you really want.
From there get an Offy intake:
https://www.summitracing.com/parts/ofy-5...ASABEgJiJPD_BwE(you can find them anywhere. Try Ebay as well)
A Holley 390 CFM 4 bbl:
http://www.jegs.com/i/Holley/510/0-8007/...AyABEgIrc_D_BwEOR
http://fitechefi.com/Then add in a cam, HEI, and exhaust system.
Odd that I can't find a Langdon header anywhere right now.
She'll wake right up then. About 200-225hp, 225-250 ft-lbs. Add in the right gearing and trans and she'll move along just fine. My old 68 Camaro could run circles around my buddy's 100% stock 68 327 2bbl car.