The 303 should bolt to any 3 speed Y bell. The catch may be the input shaft length. Compare that to the length of the truck setup you have and that will let you know if you need a truck or car 3 speed bellhousing. Compare the clutch spline and diameter and pressure plate bolt pattern. That will let you know if the clutch will work. The clutch fork you have will only work with truck bellhousings.
There could be other issues but they should be very minor because I believe the 303 was used only one year with Y blocks, and that was '64, in trucks so odds are that it will not be for a Y. I'm not 100% sure about that, though.
Lawrenceville, GA