is there a differance between chevy and gmc beds

[68GMC454]

last week i had some guy come over and look at my 68..i told him about tit haveuing a chevy tailgate..but i had noticed when i bought the truck last yr somebody had filled in the holes where some trim had been at..how could i notice,,used bondo, and did a bad job smoothing it out..then painted it white...anyway..lookking at it closer, i think the whole bed is from a chevy truck..because the cab and front fenders have no trim hole...and since the inside cab paint and under the hood paint is the same color, i figure they are the original truck..now wether it has been wrecked or just rusted otu i dont know,,i wil have to go look at the frame today...but i think its just a bed swap..the lkeast they could have done was put in good wood for the floor..im through trying to sell the truck, so i need to know if i need to swap the bed out to a gmc one, or just the tail gate...thanks for any info
billy