"What kind of HP is required for an 8 row unit?"

I think Jim will tell ya around 10 hp/row.....   We pulled 24  unit rig with a 8970 FNH FWA (210 pto)  on about 250 acres.  It worked.........ok......., but rented a red tractor with 30 more horses cuz it got wet (really wet) and the 8970 was squirmin to get the job done.    Can't remember the model number but 240 horses was for sure all that was needed.

Its one of the nice features of the pluribus====Low hp and low fuel consumption to get the tillage done.