I think you still need to line the dots up whenever you install a new chain. Set the distributor timing later. Reason being it is really easy to get a slant six chain one tooth off if you don't carefully line the dots up. Happened to me once with a rebuilt slant six long block that I bought because I needed a quick replacement (by which I mean the old motor died and I needed to get it back on the road the next day). Ran smooth but was way low on power, played around with it, finally bit the bullet and removed the timing cover and found out the dots didn't quite line up and the chain was one tooth off. I'm thinking that issue would not be readily seen if the marks were at ten and ten.
Now if you're leaving the old chain on, and the motor ran well, no need to worry about it.
Edit PS: I think I jumped in a bit too quick, assuming the OP was going to replace the chain. I agree that seeing the marks at ten and ten does not indicate a problem.