Hey Denny hows things? Those heads were used on the 410's. But also 352, 390, and 428. And the block C6ME-A is listed for a 410. But also listed for a 390,428,330HD and 360. So check the bore and wall cores inside the freeze plugs to confirm. Also look for "IU" on the crank for a 410 crank. Should be on the 7th counterweight from the front. The 6L10 is the date code of 66/Nov/10th. The "A" offhand think was just an internal identifier but not positive. What is the date code on the heads? Should be between the center two valve springs. The original slugs would have 410 on them also. Also on the heads I have two listings for that casting. First the 66-68 390 with 67-70 cc heads and thermoactor. Second the std listing for the 67 352, 390, 410 and 428 with 71-74 cc heads. Let me know what else you need. G.