Any of the '67 -'70 400 72cc (actually between 72 and 78) big-valve heads will get you the 9 to 9.5:1 ratio with dished pistons. Some have nearly 80ccs of volume and can put you at 9.5 without a dish. Look for casting #670 ('67), #16 ('68), #48 and #62 ('69), and finally #12 and #13 ('70). The '69 #62 will usually be about 75cc or more, and the '70 #13 will be at least 78cc (best choice).
Another route would be to use the '75 5C or '76 -'77 6X 350 heads. Both should have a '4' stamped on the 'accessory' boss next to the valvecover rail to ID the smaller 92 to 94cc chamber volume as compared to the 98 to 101cc 400 heads stamped '8'. You will have to mill these heads pretty much to the max of about .060" to get into the low 80cc range (intake side of heads need to be milled too for intake fit) to see 9:1 on a 400 engine with flat-top pistons.
Use a compression calculator available for your use on a number of sites (or do the math yourself) to see exactly what volume head you need. Compression ratio also depends on how far the piston sits down from the block deck (zero-deck is best for efficiency and detonation resistance) , gasket thickness (usually .039"), as well as piston valve relief/dish volume so you must know what you have in the engine to know the proper chamber volume needed.
Let's go racing!
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