Almost forgot. An alternative to the Langdon Stovebolt cast headers is a reproduction manifold for the 292:
http://www.ebay.com/itm/Exhaust-Manifold-Made-To-Fit-John-Deere-Combines-w-292-Chevy-Engine/400750523442?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649
People have complained that the castings for these parts have some shift and will take a bit of grinding to clean them up, and the Offy intake needs a few extra gaskets between manifolds for the gap. But you don't need the coolant heat for the intake, as the passive exhaust heat will warm the Offy quite well. And of course you can use a single 2.5" exhaust system with it instead.
If you can find a HD Chevy truck with 292, those have the same manifold with EFE flapper valve on them. The HD came with a 250cfm Monojet instead of the 210cfm for SD, and the exhaust manifold had a 2.5" outlet instead of the later stock 2.25" (I think earlier 292s come with 2" manifolds no matter what capacity the truck was). That is a good cheap exhaust alternative, and will use your EFE lines to work the flapper in it for warm up.
To free up some hp, eithe replace the fixed blade fan and spacer with an electric fan(s) or replace with the later L6 truck fan that had 3 blades and a clutch:
http://www.borthautoparts.com/images/cars/chevy/1980%20Chevy%20Pick%20up%20Truck%20350%20Engine/1980-81%20Chevy%20Truck%20Engine%203%20Blade%20Clutch%20Fan%20No.H-14015379%20%20H537%20Blazer,Jimmy,Gmc%20Truck.jpg
You just need to get some shorter bolts to attach it to the water pump and pulley. For a bit less drag, you can also hunt down the truck pulley that came with the fixed fan blade before the clutch one. It is 1" greater diameter, and will be like adding an under drive pulley to the crank (since we can't do that with the L6 as the balancer is also the belt pulley). I'm not sure on the part number for this, so I can't say what years and accessories combos to look for. IntegratedJ has one of these on his Nova. The power steering and alternator belts will need to be slightly longer too.
I truly wanted dual exhaust, with quiet mufflers though. Nothing too noisy. So the offy intake, and langdon splits will work together?
I didn't know if there was any gain from using a 292 manifold. I did read someone else did that.
Electric fan would be nice honestly. I never hooked one up from scratch. But can't be that hard.
