I will be trying to playtest a Pathfinder adventure shortly. I am not familiar with the Pathfinder system, find character classes an obstacle to roleplaying, and do not have the full rules. So I am not in the best position to test the balance, but at least I can try to test the plotting. I talked with the designer and will be using the Basic Roleplaying rules.
Anyway, here are some of the house rules I'm using to try to fit these together.
Pathfinder uses levels to differentiate character abilities, but does not define these levels. Basic Roleplaying does not. Character creation requires adjustments to ensure that (1) different-level characters can be included, as appropriate (2) Basic Roleplaying characters are not too vulnerable for the Pathfinder adventure and (3) some but not all characters can use magic, or sorcery, as the case may be.
The main player characters start at 5th level in Pathfinder. They should probably start with 24 points for attributes, potentially 6 spells, and 310+INTx14 points for skills, modified for age in Basic Roleplaying. They should get the total hit points option, where they have twice as many as the default, and the skill category bonuses option, where attributes affect skills. They should require the literacy skill to read or write; if they can take language (other) as a professional skill, then they may take literacy as one.
Basic Roleplaying Pathfinder Equivalent Character Creation Stuff
Normal 1st Level 24 points for attributes; 4 spells; 250+INTx10 points for skills
Heroic 6th Level 24 for attributes; 6 spells; 325+INTx15 for skills
Epic 11th Level 24 for attributes; 8 spells; 400+INTx20 for skills.
Superhuman >16th Level 24 for attributes; 10 spells; 500+INTx25 for skills.
The magic rules do not specify who can or cannot use magic, and do not impose any special restrictions on magic users. I will restrict magic to characters with POW≥14, and the points required should balance things between magic users and non-magic users.
The allegiance rules assume random allegiance values, but I will allow the players to distribute up to 10 points between good and evil, setting aside chaotic and lawful.
Pathfinder uses difficulty numbers, but does not define these numbers. Basic Roleplaying uses difficulty multipliers. In some cases, it also makes sense to apply difficulty additions.
Basic Roleplaying Pathfinder Equivalent
Easy x2 Difficulty Class 5
Normal x1 Difficulty Class 10
Hard x1/2 Difficulty Class 15
Very Hard x1/4 Difficulty Class 20
Impossible Difficulty Class 30
There are certain exceptions to these difficulty numbers.
The following optional rules are in play:
Point-Based Character Creation, p. 19. This replaces rolling for attributes.
Total Hit Points, p. 30. This gives the characters a better chance of survival.
Increased Personal Skill Points, p. 24. This gives higher-level characters extra personal skill points, as well as professional ones.
Skill Category Bonuses, pp. 20, 31, 48. This applies attribute modifies to the skills.
Freeform Professions, p. 41. Because.
Literacy, p. 67. Because Medieval.
Distinctive Features, pp. 34, 35. Because.
Allegiance, p. 315. Alignment.
Power Use in the Action Phase, p. 189. I'm not sure how to do Initiative, but this seems appropriate.