[Swiftshifter68]

Agree on using something "lower-rise" for an intake manifold, hard to go wrong with a simple, $50 Edelbrock Performer. Regarding 327 vs. 350, look and see if your harmonic balancer is retained with a center bolt or is it just pressed on? In the top-rear of the engine, just behind the distributor, is there an appx. 1 1/16" boss/port/opening (on the same plane as the distributor opening), either plugged with a freeze plug or still featuring the little PCV "road draft tube" spigot/hose, a.k.a. crankcase pressure just exits down onto the center of the highway lane as you drive. Also, get the block casting number, found on the rear bellhousing flange, can be reached from the top if you've got stretchy arms and/or a mirror-lit-with-a-flashlight. Check the # against the internet and you should get a pretty definitive answer (although over the years, these big trucks were just "tools/machinery", so a replacement 'crate' 350cid could very easily been swapped in). Good luck!