It doesn't have to Specifically for a 360. The brackets are the same for the 304 and 401.
I wouldn't go as far as saying the aluminum doesn't hold up. I have 4 AMC V8 engines 2 304's and 2 360's the factory PS brackets are holding up well. I'd say its more of the care they get from the owners, than the part failing.
Sorry none are for sale.
1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1980 CJ5 trail Jeep.
1989 YJ the CJ to YJ.