So I'm on to the building the top end of my motor and I'm putting on a Edelbrock performer 390 intake on with Fel pro gaskets and I can't get the bolts on all 4 corners to line up straight. I notices that the intake was about an 1/8 " higher than the head surface for the valve cover to seal. Now I managed to get 3 out of 4 of the bolts in on the corners (not without a struggle) but the 4th would not line up. It wouldn't go so hesitantly I ripped it off silicone sealing and all!! Anyways I removed all the silicone and gaskets and placed just the intake on the bare heads and it bolted up fine and the two mated surfaces for the intake and head were flush and there was a 1/8 gap under the front and back where the gaskets lay. So it seems the two side gaskets are what are causing the intake to sit too high and holes to not match. Now is there a different thinner type gasket I should use (special Edelbrock maybe) or is this a problem with the head sides needing to be machined because someone might of shaved the base of the heads??? Sorry for the long post

 

Sounds like the block and heads were milled enough at some point to create issues for the intake. I would lay your old intake up and verify there is a difference between the two. If the old one lays in place much better then it was likely milled to compensate for the block and heads having been milled.

 

Sounds pretty normal - in a bad way - to me. I fight like crazy to get intakes to fit these things, and I build more of them than anybody. I'll tell you how I do it... this is gonna hurt...

Take a couple clean new gaskets and mount them to the heads.

Lightly set the intake in place - dry - no sealant anywhere - this is only a test.

Install the distributor as a locating pin, if it's not properly centered nothing else matters.
Now use a rubber mallet to knock the intake around until you can level the "china walls" - the places where the end seals would go - the gap should be even side to side.

Now take a feeler guage set and check for clearance at the upper and lower edge of each corner of the intake - - upper left front, lower left front, upper right front, lower right front, etc. I write the values on the intake with a Sharpie.

In a perfect world the values should be .010 or less all around. This only happens to other people - never me. I always end up with wide variations. The bridgeport mill will reduce or eliminate these, but your machinist will give you crazy looks when you tell him to remove (for example) .012 from the upper left front corner, .008 at the upper rear left corner and none at the lower.... Of course he cannot mill a corkscrew shape, but he can get a target that reduces the variances into the working range.

Some guys don't like to mill intakes and want to do all the work on the heads. Their idea is that it make the intake unusable for other future builds. I don't care - I want to the intake to fit the engine I'm working on now.