Before I started on the rings I'd check for a ridge -- if it is less than a couple thousandths, you can ignore it, I think. If more, you probably need to sleeve and rebore rather than just stuff new rings in.
To check, just scrape you fingernail up the side of the cylinder bore on a cylinder with the piston down -- my guess is that you will find a barely perceptible ridge about 3 mm or so from the top. If it stops your fingernail, you want to use the reamer to cut it off JUST enough to let the rings pop over it. If it won't catch and hold your fingernail, best to leave it alone and just push the pistons out, the rings will jump it.
What you want to avoid at all costs is cutting enough material out to leave a rigde the other way -- wider at the top -- which will make it impossible to re-install the pistons.
Too much advice?!?>
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!