it's goin to require machine work etc to get the roller installed properly...
also the cam will probably require different springs. etc.
just swapping the cam you can probably gain some HP maybe 50 if you are lucky
best bet, in my opinion if you are going to all that trouble that route is to do the heads as well as cam. full port job on the X heads or upgrade to big port heads W2's / etc but then you will need headers/intake too and possibly oiling system mods if you want to shift at 7500rpms etc
just a cam will be a slight difference. just a roller cam upgrade will require lots of parts and machining so that's too much for just a slight HP increase in my opinion if that makes sense