Looks like a few of you already beat me to it on this one, but I'll add my $.02 anyway to back them up.
Just to clear up some confusion… the del-a-lum bushings referred to are control arm bushings that are solid with a nylon insert for low friction and wear properties. These are great for handling by the way, and don't hurt the ride.
As far as the body mounts, you want solid aluminium bushings. Not rubber, not polyurethane. Why? Both rubber and poly flex. Since the front to rear subframes are now tied together, that flexing motion in front becomes a huge moment arm at the rear. Over time, you'll fatigue where the rear subframe meets the body floor pan. So the end result will be the connector weld breaking? Probably not, but it's worse than that. What will happen is micro-cracking on the floor pan next to the weld where the rear subframe meets it. Not a good situation (they'll get bigger over time).
Both DSE and Competition Engineering sell solid bushings which they say are required for use with subframe connectors.
The other point would be that poly is not gong to last forever, and as you said, it'll be a bear to replace them unless you cut your connectors off. The solid aluminium with a coating should last the longest.
I replaced mine with solid aluminium and there was no noticeable harshness difference before and after. These will also improve handing and make the steering feel more connected. Unless you're doing a stock restoration, I'd avoid rubber or poly mounts regardless of using subframe connectors. Just stay away from stiff shocks and springs - your ride should be very nice.
