Deere did not publish a Service Manual for the 620 or 630, told everyone to use the 60 manual and I imagine they sent out Bulletins to cover the necessary changes. Torques, etc. will be the same as with a 60.
I buy my manuals for this vintage of tractors from Davenport Tractor.
The Technical Writers were busy working on manuals for the new generation tractors is why there is not a manual for the 620/630.