Correct alternator

Hi, First post in this section. I need to replace a kaput alternator on a 1.8 non aircon freelander 2001 Yreg and wondered if all the cheep used ones on ebay from rover 25's and 75's fit straight on or if the mounts or pully are different or not. Seen some used but working for £20ish delivered or a spanking new one from paddocks for £130 (ouch). I know there are two types a 90amp non aircon and 105amp aircon but wondered if the difference was just the output and not the fitment? Thanks