Probably needs a overhaul & a new slip ring [the bit the brushes run on]
1, IIRC when my 100amp was fitted we had to realign the rear of the casing to set the mounting lugs correctly
2, connectors are different marrelli uses ring terminals on end of the cables [your existing is probably like that already]
3, Marrelli are better in my opinion, there's another thread about alts on here with more info re- Lucas alts
4, IIRC mine was uprated to battery & starter.
hth