If the truck is original leaf rear suspensuion truck then G70 should be listed on the glovebox door, see if the rear shackle brackets are riveted or bolted ot the frame rails back there. 11.5" is normal stock height of front bumper to ground.
You cannot have G60 on a leaf truck, it was not available with leaf type rear suspensnion, G60 is the half leaf looking thing that is on each side of the axle and connected at the rear of the frame rails and extends down to the axle tubes on both sides.
This was auxilliary rear suspension and only available on coil spring type rear trucks.
Original factory installed tires were 31" on these trucks, 8.00-15 was the size in the early years 67-69 or 70, then size markings style changed again soonafter. If the truck is a true cab and chassis C10, then the model number wil be CS or CE10903, can find this on the glovebox door or writeen across the very top of the firewall in plain sight under the hood and sometimes alos on the backside of the very last rear frame crossmember.
If it ends with 34 then its a factory fleetside and if its 04 then it is a factory stepside.
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A 68 C-10 panel and a 68 dually C-30 dump truck and a couple 71/72 chassis projects.
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