That's fantastic thanks guys! - Ive just bought one from a 660 on ebay.

Something isn't adding up. If the particles you showed in your picture where magnetic then they weren't from the sand blasting material as that tends to be glass beads of different grit, which are not magnetic.

If the particles were not magnetic then you are probably ok, unless they were aluminum or brass/copper, which would indicate a different problem. When you get the engine back together I would do a short oil & filter change with a dino oil and see if anything shows up in the oil filter.

The other thing to try is a big magnet on the side of the oil tank to collect particles as they pass. If the magnet is strong enough it will go through the oil tank and still impart a draw inside. Even better is a "cow" magnet, the ones that are shoved down cows throats to stop any metal wire or such from getting into there lower tract, cows tend to eat junk. They are about 1/2" dia x 3inches long and will fit inside the tank, just need a way to fish it out to inspect and clean. That will give you a good idea if the particles are continuing or if it just was from previous work/wear and now finally getting cleaned out.

I'd put fresh oil in ,run for 150-250km, then drain in a clear jug, let sit for a day or 2 so junk can settle(you can then see what's in it), then slowly pour most of the top clean oil back in, this way you don't waste so much oil. Just watch when pouring to stop when the dirt starts to pour out. I run the oil through a milk pipeline filter(again cow country stuff) when doing this also.

And finally, the pump 660 (5LP) fits in the 600 (3AJ)?
I have the same problem.

No , one bolt is a couple mm off, When I posted that I had put a 660 pump in a 600 and quickly started 2 bolts to verify. Well it did fit to that point, but had I tried the last bolt, I would have seen that it was off. That one bolt is the only difference, otherwise they fit and possibly could be run with just the 2 bolts, questionable for good sealing though. The 3rd bolt hole can be slotted in the 660 pump also, then all three bolts will work and the pump used in a 600. I want to make sure that info is cleared up.

One thing that I did uncover is that there is actually 3 , not just 2 , different size (flow/volume) pumps. The 34L, 1VJ , and the 3AJ . The 1VJ is probably plenty and looks to flow approx 1/3 more than the 34, then the 3aj is maybe double the 34 pump. You will need a 3AJ gear for the 2 bigger pumps.

Thanks for the clarification.