Re: Gunslinger and other classes [PF to 3.5]
Somehow, despite what I am about to say; it's really going to come down to opinion.
In general, it is perceived that if you place the two editions side by side (Pathfinder and D&D 3.5), that things (especially races) in Pathfinder are stronger than their 3.5 counterparts.
The Gunslinger and all of the other standard classes from Pathfinder can be made backwards compatible to 3.5, however; you will need to do some comparative house keeping first.
One of the most important items is Grit. Actually this is likely to be the single biggest difficulty at all. No class (or at least no official class) gets "per encounter" abilities in 3.5. This was a feature of 4th edition. Grit essentially functions as a narrative-comical way of regenerating powers and abilities. In doing some translation to make it 3.5 viable, you would have to find a way to tone this down compared to some sort of similar class structure (perhaps comparing to a Ranger->Arcane Archer?)
Classes like the Inquisitor, Cavalier and Magus are pretty simple to handle, because they already exist in 3.5 as prestige classes. This means building a simple character that is optimized for that prestige class, then figuring out which parts the 3.5 version never gets - take them out of the PF version.. and call it a single class and you're done.