Hello folks! Sorry I got to this thread late. Here's what I did in my '70 std. I mounted Corbeau seats to the stock track/seat base assemblies. The cross bars are plain black steel (water) pipe (schedule 40??) and the steel uprights were cut from flat steel 2"x1/4" that i found lying around. The seats bolt through both cross bars. Full slider action retained! and they are very strong (but a little heavier than I expected!
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Good luck!
Dave