My alternator failed recently, resulting in me having to get recovered to home. Got a replacement no probs from an ebay vendor for £45 with 1 month & was obviously well pleased. (I'll try to find the vendor again & update the post).
Upon removing the old alternator, I could not get it past the driveshaft as the gap between driveshaft & bulkhead is much too small, also the replacement alternator was slightly more bulky - (fatter casing).
Method - Car front end is supported completely on axle stands -then support engine/Gbox from below (I used 2 or 3 good bottle jacks for this), remove both through bolts from both rear engine mounts, loosen top engine mount only as much as required & allow engine to drop slightly by letting jacks down very carefully. I also used a large pinchbar to lever engine forward slightly. With an assistant you'll find that you can get the required clearance between driveshaft & bulkhead to get the job done.