The Pathfinder Core Rules have been modified as follows:
PF races stand. Players may pay most other races although powerful races can be reduced to a template or level adjustment. Discuss with the GM.
Classes: As the PF rules
Characters gain a feat every odd level instead of every three levels.
Skills: As the PF rules
Feats: Most feats work as is with the following modifications.
Item Creation Feats: There is no longer a need to take item creation feats. Instead items are created based on Spellcraft and the appropriate Craft skill. A PC knows the formula to create a magic item equal to their ranks in Spellcraft. The appropiate amount of gold must still be spent.
Meta-Magic Feats: Characters may spontaneously use a Meta-Magic feat 3/day. After that they can use them with their normal level adjustment.
Criticals: Critical hits are automatically confirmed. Weapons threaten ranges are the same although items that double the threaten range instead add one to the range. Thus a Greatsword starts with Crit 19-20 and if Improved Critical and Keen is added to the weapon it's crit range becomes 17-20.