Intake not seating down between heads

[BOWTECH.JUSTICE]

Following up to my previous thread of my 1992, 4.3 mercruiser, serial # D829937. I got a rebuilt through Summit Racing and my intake won't seat down between the heads as it is hitting the top unmachined part of the top rail of the heads. The heads on the old and the new heads have different dimensions on the machined face for the intake. Old face is about 2.75" wide of the machined face and the new is 2.50". The top rail above the machined face measures 1/2" on old and 3/4" on new. Cast #s for the old heads are 10144103, new-14094768. Cast #' for old block are 10172756, new-10105867. I'm being told from Summit, and ATK the engine mfr., that for some unknown reason my old motor has these odd ball heads and intake. I guess my questions are- is this true? Does anybody know why? and is my best option just to bite the bullet and add more to the cost by buying an intake?
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