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I'm not an expert either but I'll share what I've learned while working on my current 4.1 build. The length of the pushrod is determined by lifter preload which on my comp cam kit from full throttle should be .020-.040". You check this by marking the push rod at two different positions and measure the distance between the marks. This is explained in more detail in the installation instructions from Comp cams that came with the kit. The pushrods in my kit were 8.225" long X5\16diam. X .080 wall thickness.
Also, if your cam has a lift of .510" or more your exhaust valve guides need to be modified so you can use a positive type seal that also requires replacing the stock style exhaust valve. I've read comments that this isn't really necessary if you just stay with the stock exhaust valve setup but people like turbofabricator and my machinist strongly recommend machining the valve guide and adding a seal with a new aftermarket style valve. I did it.
MLH
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white '87 T, lowered, "B" brakes, GW susp, SP204/214,RJC plate, PT6776RS, 2.75" exhaust w/test pipe, 60's, Gen II trans, extender extreme, SMC Alky, SM2, BstC., FMIC, 3K stall.
4.1L build going together slowly.
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