Look into dirt modified race shocks and springs from places like Speedway Motors, Day Motorsports, JR Motorsports, Performance Bodies, etc. They offer numerous soft springs and shocks required for modified 4 bar rear setups.
With your combo of monoleaf and coilover, you need to know and calculate the total rate of both springs, and buy your coils accordingly. You probably don't want much more than 200 - 225 total combination max.
Also consider split valve shocks from Bilstein, Afco, Integra, Pro or others. You can get 7" 8" or 9" shocks in various rates such as 30-50, (also known as 3-5) which is easier compression - stiffer rebound which will soften up your ride. We call them "tie down" shocks because they let the car settle easy then let it raise back up at a slower pace. There are numerous rates available ranging from 90-10 to 10-90.
Remember that Bilsteins the numbers are backwards, so it will be 5-3, five rebound three compression.
Speedway Motors also has Hot Rod suspension stuff.