BW stopped the investment casting production and continued the production with regular sand casting to lower the cost of each unit. Thats why the surface finish is terrible compared to the older ones. All later model BWs are supplied with these sand casted turbine housings.

Remember that Garrett turbine housings are cast iron, vs BW cast stainless steel = MUCH higher pouring temps and MUCH harder to get a nice finish. Trust me, I have done some work in a foundary.

The compressor cover is slightly different as the 7670 has a larger compressor than the 7064...

My 7670 is the same as yours. It is, however, much better finished inside than outside.