Ok you are probably thinking of something like Transdapt and several others make.
I checked the transdapt sight http://www.tdperformance.com/pdfs/34...Swapmounts.pdf
and didn't spot one for a smallblock mopar but it shouldn't mean that you can't come up with something on your own.
Most of the ones I have seen are made out of 1-1/2 mild steel tubing.
If you don't have someone who can bend the tubing you might check out this one with the idea of modifying it to fit your engine and mounts.
50 bucks plus shipping might solve some problems.
By snooping through and engine mount catalog you should be able to find some pretty clean mounts to fit your engine and help make building the brackets to your crossmember easier. If I remember correctly the mounts for a small block in a 69 Barracuda were pretty simple.