gen 1 sbc head question

[TylerT/AZ28]

ive come across this once or twice never understood the reasoning behind it, while replacing valve seals the intake and exhaust side are said to require different part numbers, for example this is your intake side http://www.summitracing.com/parts/fe...make/chevrolet

and this is exhaust side
http://www.summitracing.com/parts/fel-ss72526

every head ive pulled apart the plastic looking seals are always semi melted the umbrella ones are always in tact, why cant i just use the umbrella seals.

[hoogiesngrinderz]

Both are umbrella type seals but are generally different material, the exhaust set having to stand up to higher temperatures. FEL-PRO Part # SS72877 are the hi-temp option.

Older heads are generally umbrella while newer heads are positive lock, meaning they don't move with the valve.

[TylerT/AZ28]

the positive lock are the blue ones for intake valves? and the high temp ones for exhaust would work on any factory sbc head pretty much?