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I'm no expert on chevy heads_(I never built a "race" motor or got into valve size increases--I just put rebuilt stock or good used heads on quite a few motors--),but I do know most of the pre 70 ones with the spark plugs that were gasketed rather than the tapered seat "peanut"plug ones were usually smaller chamber,which=higher compression ratio,and are heavier castings than the ones in the 70's and up..
Those(early) heads might raise the compression to 10.5 or higher-(varies with piston type,etc)-great for more power and tourque,they ruled the streets back in their day!-you could get them with screw in studs and guide plates..but on a motor run on todays "low" octane fuel,most motors knock and ping to death on 93 octane pump gas,and unless you run race fuel with the gas,it wont like it..detune it enough not to ping so it will live,and it wont go much better than any smogger 350 chevy in most trucks run..the older heads might lack the "accessory" holes in the ends for power steering brackets,altenator,etc..best to look FIRST BEFORE the heads go on!(dont ask me how I know!
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I'd say unless you plan on running high octane fuel or a mix of race fuel and gas,then the heads giving the higher compression will give the most power and torque,but will be costly to run..might be better to go with heads that will retain a nearly stock compression ratio,and "tune" them with the camshaft to the motor.I think the CAM does more to affect performance than any changes in valve sizes in most cases..big valves means slower airflow velocity thru the heads--great volume for high revs,but might make a "bogg" at low rpm acceleration..a small valve and intake ports keep things moving quickly,and it makes for smoother low speed running and more low end tourque--what you want in a truck,especially if you want to crawl off road..you need good tourque just above idle and good throttle response to maintain control in off road manuvers..
..I've had some pretty impressive rides in stock corvettes with 327/375 hp motors in them--that "Duntov" camshaft they had in them REALLY woke up a pretty much stock chevy small block with the high compression ratios they could use back in the 60's when we had 100 octane leaded gasoline available for less than 50 cents a gallon!....but that same motor today in my friends vette needs 93 octane plus race fuel or octane booster to get anywhere near the same performance on todays gas..and though its in perfect condition still,according to him"it doesn't run like it used too"--he blames the fuel,and I agree--its all formulated for EFI cars now,us dinosours with carbs still are probably blaming the carbs for the lousy mileage and performance--when its the FUEL that is the problem!..
So unless they bring back 100 octane fuel soon(doubtful)--I'd stay with heads like the motor came with,maybe the ones with larger valves if you want it to revv hi( not what you want in a truck,especially a 4x4 )---but I've found the "small" valve heads give better low end tourque than any other...
One of the strongest 350's I had was one with the "small" valves,and a 2 bbl. carb and intake off an old 283!-
-I could leave my truck in 3rd until it was going 10mph then step on the gas and GO,no jerking or hesitating--I swappen in a 4 bbl carter AFB and aluminum intake,and that killed all the low end..driving the truck after the swap was much more of a chore,and a lot jerkier,and trickier not to stall it when letting out the clutch...I never realized the "speed" of the air/fuel mix going thru the heads and motor could affect the "way" an engine pulls under a load like it does..I should have left the 283 - 2 bbl setup on it--it was better!...
I'd say the newer heads might be the best comprimise--or wichever ones aren't cracked!
