This is from the 1960 shop manual. "Springs should be compressed to 1 27/32" at which height it should check 65 pounds for Thristmaster 235 engines and 78 pounds for jobmaster 261 engines. Weak springs affect power and economy and should be replaced if not within 10 pounds of the above load."
I'm also building a 59 261 with an 848 head. I'm using 1.94 powerglide intake valves, 261 springs, and 261 exhaust stellite valves. Also from the 1960 manual "261 exhaust valves have hardened stellite face and hardened valve stem tips."
I also had a used rocker assembly. The rocker arms were all in great shape, but the shafts were quite worn. $32.00 for a pair from NAPA and they'll be here in a week.
