I have a set of Ron's headers. I'm sure his design, like most (all?) others require spark plug access from underneath. Of course its a hassle to have to get under the car but I can actually replace the plugs in my Pantera faster than I can in my neighbors '70 Mach 1 with a 351C. You'll also need to think about plug wire routing. Mine come from the top with Kevlar sleeves for protection. I've also heard of routing them from the bottom.
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