2 gallons of coolant out exhaust!
 

74 k10 350 New heads and gaskets, edelbrock performer Intake new gaskets. Started it up today first time and it was running fine. I glanced behind the truck and nothing but white smoke. Turned it off and looked under the headers and two puddles of green antifreeze! Checked the dipstick and it was full of water. Could it be the intake gaskets failed? Haven't done a compression check on it yet but it sounded good when it was smokin like that. Ran for about 20 seconds and all the coolant was gone!
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Re: 2 gallons of coolant out exhaust!
 

Sounds like intake or head gaskets for sure.

Re: 2 gallons of coolant out exhaust!
 

Since this happened shortly after the engine was put back together (or at least, that's what I think you are saying when you talk about new heads, intake, and gaskets), and since so much water leaked into and out of the engine in such a short time, I would look for some bolts not properly torqued, or maybe the block and/or heads were milled a lot so now the intake manifold does not sit properly, or maybe the intake is for a different generation of cylinder head.

Re: 2 gallons of coolant out exhaust!
 

did you tighten and torque the head bolts and intake bolts in the proper sequence? and use new head bolts?