What "adjustable levers" are you talking about?

If its a steel bike often you can cram a wider rear hub in no problem, I didn't bother to respace my Paramount. Not worth the effort... a lot depends on the bike though.

PS there are 8spd Sora and Ultegra 600 levers out there.

Now is a good time to be going 9spd, the new Ultegra is 10spd but the old 9spd stuff will be going for cheap pretty soon. You'd need to do the front crank, derailleur, chain, wheelset, cables and housing, bar tape, STI shifters, rear derailleur, cassette, and bottom bracket.

It would help us to know what bike you are thinking of doing this too, and the approx. vintage and what parts it has now.