Single and dual spool remote hydraulic valves are available both new and used to fit your 861. Complete units are a simple bolt-on at the accessory plate beneath the seat.
The going rate for a good used single spool valve is usually around $200 - $250, while that of a dual spool is usually $450 - $560.
Sit down before pricing new units, e.g., TISCO.
You will need a dual spool valve to operate a fully hydraulic loader and may be disappointed with the cycle time of the loader using the tractor hydraulic pump. A better set-up for a loader is a crankshaft driven front pump.