I had a different make than you, but I took mine to a radiator shop and they made a 4 core radiator that fit in it for me. However my engine made its best power in the 210 to 215 degree range and at times I had to turn the
oil cooler off as it wouldn't get above 185/190 degrees. So if your radiator is to small you may be able to buy a ready built one that will fit and take care of the problem.
Ron