Best Years for the 318 LA?

In Australia all of our late 318 in our Valiants 1977 - 78 79 80 81 were made in Brazil. They have made in brazil cast into the side of them. My machinist has sonic checked one of them and found they are a lot thicker in the bore. Maybe my mate Bewdy can shed some more light on these blocks. I have a 1979 CM Chrysler Regal with the Brazil block with edelbrock alloy heads weihand manifold and 650 AVS 2 with headers on it and as it has a 2.92 diff and very tight converter it is slow down low but when it gets up in the rev band it hauls arse for a large car.