1967 chevy c-30 tow truck

[Dropdeadfred]

hello,

this is my 1967 c30 tow truck i purchased this truck about 6 months ago after seeing it in a field.
I have replaced gas tank, carb and radiator to get it running and driving, i want to make some upgrades to the brakes and rear diff

what vehicles i should be looking for for donor parts i have read that i need to look for a crew cab dually 78-80?? i have also been told i need to look for cab and chassis donor trucks which is the right one??