In those years Chevy used the same rad for a small block or 6, so yes, you can use your rad. However, I know for the cars that the 8's had a factory shroud, so you may want to try and find a factory small block shroud for your 283, if they exist for the trucks.
The six cylinder & V8 radiators, were not the same in the '63 Chevy light-duty trucks. The standard six cylinder radiators, sat in the lower cradles on the lower flange of the radiator cross member, between the the frame rails, whereas the wider tanks of the standard radiators, in the V8-equipped trucks, sat on the top flange of the radiator cross member. In my opinion, since you are installing an era-correct 283 in your '63 Chevy truck, a factory-correct V8 Harrison 2-core, 3-core or 4-core radiator & corresponding fan shroud & shroud extensions, are appropriate.
