Yeah like i said "i don't know if it's true". If the ser1 turbo blocks do have thicker cyc walls they've probably rusted down to the same as ser2 with the extra age Anyway, there is 1 difference with the ser1 block and thats where the idler pully bolts on for the twincam head. Ser2 have a nice machined flat surface with a hole drilled and tapped ready to take an idler, but the ser1 doesn't have the machined surface but still has the drilled and tapped hole... Just another problem to overcome with fitting the twincam head... U can see in this old pic of my engine. Just saying maybe ser1 turbo had a different cast, maybe thicker, maybe thinner???? Some original photos have not been recovered yet.