[4birds]

Originally Posted by bird72

So are 72 and 71 crossovers not interchangeable? Will repro work on 71? And another puzzle: some 197 heads are drilled for 2 end exhaust bolts and some only one? what I deduce from ebay ads. I just got set that have one hole drilled, and Ram Air Ent manifolds are cast for two bolts, so I should have shop drill end hole when do heads I assume (?).

Anthony, which heads do you have? If you have 71 HO heads, you must use a 69-71 intake crossover. If you have 72 7F6 heads, you must use the 72 intake crossover, as it is different.

Are you going to use factory GM exhaust manifolds or reproductions? (or headers?) The factory exhaust manifolds on the 71-72 HO's only used 3 bolts to hold them on. That's why the 2 holes are not there in the heads. The reproduction manifolds use 5 bolts (copied from the 73-74 SD) for improved sealing. Therefore you will need to drill and tap the heads if you use the 5 bolt reproductions or headers.

The first picture is of the GM 3 bolts OE manifold. Picture #2 is a R.A.R.E. reproduction round port manifold. Pictures 3 and 4 are 72's. The last picture shows the different long slot for the crossover for 71. (the 71 197 HO heads will match this long slot)

[4birds]

1972 and later gasket on top, up to 1971 gasket on bottom.

[PAUL K]

Originally Posted by 4birds

Anthony, which heads do you have? If you have 71 HO heads, you must use a 69-71 intake crossover. If you have 72 7F6 heads, you must use the 72 intake crossover, as it is different.)

You are correct when using GM parts, however most reproduction crossovers were designed to work with either head.

[bird72]

Just to clarify 71 heads and intake is what we have. I have oversize RA Ent new manifolds. In my prior aborted HO attempt the cracked factory manifold nightmare ensued and this time decided for once repro was a functionally better route. I need a crossover, have offer on repro, so doing detective work on opinion / fit / quality, it looks nice in pic. Slight appearance differences probably would not matter to me. Of course a 71 GM one would be preferred.

I looked on ebay on 71 head pics see some have all holes (?) wondering if some 197 came double drilled and some not. Or are double ones owner modded.... I lean towards drilling head as smart, but if it is of no value and degrades head I guess I would not, but really don't care in this area also as to head "virginity" too much unless drilling is just dumb move stuff value wise. But it does seem smart engineering wise to drill for grins.