300 is doable, but I'm not sure I would call it a "budget" build. 300 N/A is also getting right on the ragged edge of a streetable Slant.

More is not always better when porting a Slant head. Be careful when choosing valve sizes too. What makes for great flow on a flow bench does not necessarily work on an engine because of the small bore.

Dig around on www.slantsix.org and you will find an engine build matrix that details many of the motors we have done.