Am replacing the flat tops with S.U. Carbs complete with manifold. Does the exhaust manifold have to be unbolted when replacing the intake manifolds? The FSM is not clear about this, and there appears to be bolts only at the top of the intake manifold.
Yes it does, and not only that, but you will have to take the manifold off and replace the gasket. i believe the 260z had the better intake manifold. i would keep that, and just transfer the carbs and balance tube from the 240 setup. you will also have to swap out the studs for the carb, I had a 3/4 spacer on my 240 manifold, but if your new setup does not then don't worry about it.
Thanks Andrei - I'll go your easy route first, although I really like the clean look of the S.U, manifold. If I decide later that I cant live with it, I will go the long route. I have the 3/4 spacers for the Carbs also.
Once you've replaced the balance tube there isn't much on the 260 intake manifold that looks "unclean". If you are still running the smog pump, the air filter for the 240z carbs doesn't have a connector for the anti-backfire valve as it was connected differently on the 240z (in series with the air injectors rather than separate). You don't need to replace the balance tube to use dometops but there are a bunch of things you'd need to plug.
I had dometop SUs on a 260z manifold with the thinner insulator blocks so longer studs weren't requried. This might not be as good as the thick blocks, though. Make sure your dometops are in good shape. Mine had a leak at the throttle shaft on the front carb (requires rebushing, not too expensive).