Gains yes... But that is one hell of an involved swap. That is a good price for them tho. Just for starters.... You would need the new upper and lower intake. A tb, all the sensors, timing cover, chain etc. New headers and exhaust Midpipe for sure. I would be tempted to say buy a block and some internals and build it up outside of the car then when it's done swap it over. Check out some of the threads regarding a 4v swap.
2003 Mach 1