Oil cooler up grade

[beavis911]

I have a '78 SC and want to replace the trombone cooler. A friend has a 25 row oil cooler that I could adapt in with a fan. The installation is not a problem, my question is that while the fittings on the cooler are 3/4" the actual oil passage is about 3/8" vs what looks to be on the trombone would be maybe 3/4" inside(haven't removed it yet). Would I have any problems with the difference in the inlet/outlet size being smaller on the cooler? This is not for track use, road only and only gets driven 2-3k miles per year. I live in the central valley of CA so it gets rather warm some times and just trying to cool things off a bit.

thanks