As HRL said, the small blocks heads are interchangeable side to side. Each head has at least one threaded port on the exhaust side of the head, typically the left head has the temperature sending unit but there is no reason that the right head could also be used for another sending unit. Chevrolet used a green single wire for the temp sender on the left, front.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy