In my 3.5e campaign we started using the wealth score instead of Gold and the wound system instead of Hit points. It is an easy conversion on the fly for everything so far.
Now we are just going to convert the characters over totally to true20. The fighter and thief were easy to convert, but am at a loss with how to port the magic over.
I was thinking about making an Arcane Magic Feat for each class (expert bardic progression, adept wizard progression, warrior paladin progression), but then was unsure how do do 'level' advancement for spell use. What if they took the feat at a level higher than first?
Then I was thinking about making the progression through spell levels based on feats, 1 level of prgression per feat. So to cast third level spells, you would have to have the first level feat and then the second level feat.
I guess you can tell by my ramblings I am at a loss on how to proceed.