Yes, you can buy just the support system. The bottom bar is machined to clear the bolt heads, so I don't think you'll be able to tie them into it. Besides the fact that drilling the holes would weaken the bar, if you used spacers under the bar to support it under the bolts, it would raise the bolt heads to the point of interfering with the shaft. I believe Rory has been using this system on his low 10 second Fairmont drag car for some time now, without any problems. So it's a good system and is probably one of the best out there without going to a TD race system. I don't know what spring pressures Rory is running in his car, but he has iron heads which help.
I should add that there's not enough room under the bar for the thicker nuts used with ARP studs. While I prefer studs, I've never had a problem with the factory hardware and had no issue or reservations about using them on this engine.