Contact "Detroit Speed", I believe that they have bottom plates for this.

 

68 or 69 should work. I don't know about Nova. The U-bolt spacing holes are the same. What will be different is the lower shock mounts. The multi lower mounts are about an 1-1 1/2" higher up than the mounting ears of the mono. How the shocks mount to the plate is different.

 

Some (if not all) of the X-body cars use an anchor plate that looks just like an F-body monoleaf plate; two ears, between which the shock mounts with a through bolt. The 75 Omega that donated my 8.5 had multis with the F-body monoleaf style plate. Easiest thing to do is just get a pair of the repro 68-69 multi plates, as long as you are planning to change to the multileaf shocks too (can't/shouldn't use mono shocks with multi plates).