Converting B/X Vancian magic to Romance of the Perilous Land points system
One of the things that differentiates Romance of the Perilous Land from many other OSR games is that it doesn't use the Vancian magic system. Instead, it uses a points based system like in Tunnels and Trolls.
In order to convert Vancian to points based as a rule of thumb double the spell's level to get its points value. Everything else behaves in the same way. So a 7th level spell would cost 14 points unless the DM decides it should be a couple of points higher or lower.
That's it really - nice and simple. This makes it easier to run a wide range of OSR adventures with the RotPL ruleset.