Harry,
My TC-157 is Rev 24 dated 2-81.
Donald T,
The parts manual calls for a "Bolt, 3/8-16 x 1-1/2 CZ, Cr-Res Truss Head Machine" for all the narrow frames from the 70 thru 125 and probably the 73 although this manual (TC-113., Rev 26 dated 6-91) shows the same PTO engagement arm as used on the 1X6/7, which is incorrect for the 73. The CZ=Cadmium or Zinc plated, Cr-Res= Cross Recess which to my knowledge would be a phillips, truss head bolt, or in your words "a big phillips head bolt".