From your pictures, I'd say pre 1986/87 on he engine. It could go back to 1968/69. It could have come from a car or truck. I have always had good luck with AC plugs. Most guys here seem to say, just use a standard plug, and not the fancy,gold filled iridum whatever ones.
If you did a search on SBC head identifcation you could find out more, If I were looking for new plugs for your engine. I'd search Autozone or a place similar, for a plug for a 1980 impala with a 350. Then 1972 pickup truck. and a couple others, see what you come up with.
If its running good with what you have stick with them.
The distributor looks like a standard GM unit with the coil on the cap.
You have way too much rubber hose for fuel line, steel is better, Given the location of the line pre filter, you could have a electric fuel pump. Carb'ed 350's have the mechanical pump under and down from the alternator.
1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1980 CJ5 trail Jeep.
1989 YJ the CJ to YJ.