anybody know, really know about coilovers?

[tmoble]

I have a 57 I'm working on, ready to do some major work. I was going to put a 4 link with panhard bar and coilovers on a 9 inch rear. I have a long time buddy that a fabricator, works on old trucks and cars, makes a living at it. He's usually not critical of anything unless he has direct knowledge of it's shortcomings. Anyway, he tells me to forget the coilovers, sez he's built several and they all bang (bottom out, I think he means?) when going over bumps or hitting dips at speed. He claims they're all like that unless a guy ponies up for Bilstein based setup. Big bux, apparently. Anybody with experience care to comment? Yea, nay or STFU?