You should be able to get 1 HP per cubic inch from this engine and still be streetable with no problem. Beyond that, you will need to decide if the mods necessary to get more HP still meets your needs for street driving. Another 50-75 HP can still be gotten with common parts, but the next 100 HP after that is going to be a little more involved as you already mentioned. If you can find the threads on here from the 250 dyno testing done a while back, you will see that this is easily obtainable with commonly avaialable components and basic block and head work. So no budget breakers to worry about and its also pump gas friendly.
