when you do imbue on Diablo 2, dont matter if item is SUPERIOR or CRACKED, in the moment you imbue, it return to natural standart base.
so irrelevant for us a superior item to imbue
what some guides says is the iLVL ( item level )
so you have more chances to get a good imbue when you using a LVL AREA 78 items, from Chaos Sanctuary Hell, not even from River of Flame which is level area 77. here link to check classic lvl area =>
https://forums.d2jsp.org/topic.php?t=17219980