I took a nap and then looked at my drawing again. It needs one additional part, a diode (shown in green) to prevent the stomp switch from back-feeding the relay.
This is getting too complicated. Leave it like your wiring instructions have it. Just don't stomp the starter with the transmission in gear.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
