I've recently been looking at the player's rules for the LotFPRPG, and I'm very impressed. This is not going to be a review, as there are many excellent ones out there if you want to look at them. Also, the Character and Magic rules are free so just go take a look at them if you haven't already.
Though I think it has its flaws, its innovations are more than enough to make me consider using it over Swords and Wizardry for Nightwick Abbey. Almost all of my houserules can carry over from S&W with no trouble.
I see no problem with switching systems at this point as they're both OSD&D in some form, but also because play has not yet begun. I'll still be using the same resources I was already using for monsters, treasure, and dungeon stocking since I only have the free player rules. Also, I'm not going to take his advice on monsters. I like Orcs. Sue me.