Wayne Marshall brings enlightenment viz "junglists" and "gardenists":
"i believe what you're looking for is arnette gardens--which is located in trench town, not far from tivoli gardens. both "gardens"--a term created by the political parties that built and named these public housing schemes (and made sure that their "supporters" were housed in them)--are located in west kingston, downtown. i believe the two areas were (and still are) politically antagonistic garrison communities. tivoli, which was created by plowing over longstanding squatters' developments, was and has always been the base of seaga, who as you note is the reagan-ally that many jamaicans blame for the country's ultra-violent, gun-saturated politics. people still big up "jungle" and "junglists" on tapes and records and such. don't think i've ever heard "gardenist"! so, i'm afraid that they're all "gardenists," in a sense--even the "junglists." that means there's less poetry--and perhaps politics--to the resonance of the term."
Arnette Gardens! Of course, of course. (John Eden confirms the derivation, but spells it Arnett Gardens.)
Wayne Marshall, incidentally, isn't that Wayne Marshall, but he's the real (or a real) Wayne Marshall, he points out, "cos the the dancehall singjay adopted "marshall" because he thought it a better stage name than his real name, wayne mitchell". Our Wayne is an academic whose field of expertise includes Jamaican music, bizarrely enough.
Somehow I imagine the support in particular areas of Kingston for one party or the other was probably fairly non-ideological: in other words, less about policies or values than getting your people into power to get hold of the spoils--patronage, funding, etc, etc. Bit like how the old "machine" politics used to operate in American cities.
(Seaga, incidentally, although pro-America, had a past of being deeply involved in the Jamaican music industry).