helping friend with a 78' dodge pickup with a 400.

rear cylinders (7&8) are miss firing, exhaust temp around 200*.
the rest average 400* to 500*.(has headers)

comp. test showed 90# first pump,then went to 120#,on all cylinders.

he has replaced plugs, wires,cap & rotor and also put a new edelbrock (carter) carburetor on it.

i tried spraying carb cleaner around the base of carb,intake manifold and under the intake (but don't believe i was able to get the straw under very far) was not able to get the engine to pick up the rear cylinder's.

pulled the intake, tub doesn't show any obvious areas of leakage.

checked cam and lifters,all are good.

checked lifter pre-load, plunger close to bottoming.(i installed .015 shims under rocker shaft's,engine not back together yet....not sure what to do with the intake)

cleaned the intake (stock cast iron 4-bbl), with straight edge,can get .004 - .005 between the ports on the 1,3,5,7 side, and between 2&4 on the other side.

should i replace the intake?

have it surfaced?

or put it back on with the 6-pak thin gaskets on each side of the intake?