I'm sorry, but you are wrong about the balancers. The later 360/390 engines used the SAME balancer as a 428CJ. I have a 428 CJ 68 1/2 Mustang-factory. I have another of the same car in my shop that I am restoring for a customer. I also have a 428 in my 69 F100. I deal in these parts, have bought many FE parts and such. An example, my F100 had a 360. When I removed the 360 which was original, never opened up, I removed the stock balancer. It is the exact balancer that the 428 engines use. it's not the e arly FE balancers that had the pulley built on to them. It is a thick balncer with the EXACT same numbers on the balancer. I have seen the exact same balancer sell at Carlisle and the like, listed as 390/428 balncer. They are the same. I realize that the 428 and 410 are externally balanced. I know the others are internally done so, but in 69 an up, the balncers are the same and the bulk of the balance is handled by the flywheel.