I'm trying to build a 1969 daily that I can take to the drag strip once in a while. I was set on getting 4 1/2 leaf mid eyes with polyurethane bushings until I found out WCCC is the only place that sells the polyurethane bushings for Cougars, so it would cost around $160 (with shipping) to get polyurethane. My first question is is it a good idea to replace the shackles ($60) no matter what (I live in the rust belt BTW)? Second question, is it worth the extra $50 ish bucks to get the Del-A-Lums? Third if I got the Del-A-Lums should I only get 4 leaf mid eyes since the Del-A-Lums are stiffer? Fourth I've seen one or two posts saying the engineers designed the rear end with rubber bushings in mind, so something solid like Del-A-Lums could tear the rear end up. Is this true?