The older cranks would be fine up to 8 speed, and maybe even 9/10 speed.

From what I understand, the chains for 9 and 10 speed are narrower on the outside, but the inside is the same. I know 10 speed chainrings are closer together, but I don't know if it is essential, or just optimal.

Sorry the information wasn't more beneficial, but you should probably still keep your eyes open for 8 speed DA shifters on Ebay if that holds any interest... It seems like I see them occasionally. Then all you should need is cable stops for the down tube braze-ons and a rear wheel. BTW - I believe the spacing on cassettes was the same for DA and other lines, it is just the RD and shifters that Shimano made to a different spec.