Ultimately, the easiest thing to do is get a carb tank since your bike is carb. Mounting will vary by the model and year. The 01 Heritage Softail tank that I am installing works very well. It gives it a lift in the front (that I really like) and goes through the existing bolt holes on my 02 sporty frame. I will have to drill and tap on the backbone for the rear set screw, but that's an easy and pretty small job.
The year that fits best in my opinion is the one that is in the best shape for the least money. Craigslist and eBay.