The 305 TPI head is the same as a 350TPI head other than the small er combustion chamber and the smaller intake valve.
If you want your 350 to have the same cr is stock you can.
rebuild the 350 using a dished piston and the 305 heads as is
Or rework the 305 heads for larger 350 sized valves. (1.94x 1.60) This rework will involve slightly clearanceing the chamber wall around the valve which in itself will make the chamber larger. (probabily around 62cc).
Now you have a perfectly usable "350 head"