Another vote for the adj mechanical, mine have banana groove shafts. I put together a driver 69, 340 4spd swinger. Put 5,500 miles on it this summer, rockers are the furthest thing from a issue in my mind. I did the whole car that way, nothing to fail......drove it 16hrs rnd trip this summer. Didn’t want anything to fail that could fail for no reason. Mechanical all the way. Just my opinion for wiw