wazzu70, I stayed with US S50/S52 33mm lifters due to the fact that I kept the M42 cams and had them reground. The Euro Lifters are shim over bucket not hydraulic which would mean a completely different set of cams. However, changing from just the stock 35mm to 33mm is a huge weight savings all the way around from buckets, springs, seats, retainers, keepers and don't forget the 6mm valves.
Cheers,
~Ralph