I believe you can get a assortment of radiator sizes from Jegs, Summit and Speedway Motors... Here's one from speed way for ~130
https://www.speedwaymotors.com/Speed...tors,3557.html
They also have ones where you weld on the fittings which may be better eliminating the radiator cap.
Big thing you want to be mindful about is how the radiator is made...
More cores are not better. You want 2 cores that are 1 inch thick....
Here is a good article.
The Last Radiator You Need For Your 1955, 1956 or 1957 Chevy (I also have a 57 Chevy)