I have a sagging Rear spring under my mono spring car. My 10 bolt rear "supposedly" will only accept the mono springs. Is that a correct statement? If so, can someone give me some ideas for some good replacement springs and if any of the multileaf springs will fit on the 10 bolt perches. Thanks.

You can use multi-leaf springs with your mono-leaf rear, with some modifications. First, you should use the multi-leaf lower shock mount/spring plates(they will locate the lower shock mounting point at the correct height) Of course this means switching to multi-leaf shocks too. Second, use u-bolts in place of the t-nuts, much stronger and lower plate will now not draw up to axle housing mount so the u-bolts are much safer. Third, the multi-leaf springs are wider than the mono springs are so you will have to trim the sides of the rubber pad to get it all to fit in there. This is how my car was before I switched to a 8.5" multi-leaf housing.

To help it all stay together, I made up metal spacers to fill the gap between the perch and the lower plates. Make the thickness so the rubber compresses a bit when you tighten everything up.