Bicycle Mechanics - jury rig barrel adjuster?

Anyone have an idea to help convert a vintage shimano 600 rear derailleur into index? I was recently given a pair of 7 speed shift levers to replace the old friction set. The difficulty I have is that the derailleur was not built with a barrel adjuster in the rear where the cable passes through to the cable lock nut. There is a space that , on later models, was threaded to accept an adjuster. Any thoughts on rigging something up to provide a tension adjuster of some sort to allow fine tuning for the index?

You can put adjusters in line near the shifters, or use adjustable cable stops on the downtube.

You can buy barrel adjusters which slips into cable stops. That might work. And there's always those in-line adjusters that can be used in the derailleur cable housing as well.
I assume you're using down tube shifters.

yes, I am using downtbe shifters. Where do I find these "alternate" type of adjusters? ( I don't have cable stops on the down tube- shifters are braze -ons.

yes, I am using downtbe shifters. Where do I find these "alternate" type of adjusters? ( I don't have cable stops on the down tube- shifters are braze -ons.

There's a cable stop right above the derailleur on the chain stay.

You can find in-line adjusters here. (http://www.loosescrews.com/index.cgi?d=single&c=Cable/Casing&sc=Barrel%20Adjusters&tc=&item_id=LS-1404RB&id=475262429750)

In your case, I'm thinking the easiest and most cost effective solution would be to buy a replacement rear derailleur that has the adjuster attached. Talk to enough bicycle nuts and you'll find one for cheap or maybe even free.

You can't install an inline adjuster near the shifter because it's all bare cable. An adjuster on the chain stay cable stop probably isn't going to work.

Adding a barrel adjuster doesn't make a derailer designed for friction shifters an index derailer, but you might get lucky. I read that an SX series Simplex derailer will index with 7 speed Shimano shifters and freewheel or cassette. Simplex never made an index derailer to my knowlege, but the SX derailers have a barrel adjuster.

Thanks for all the advice. I think I will consider a new/used derailleur. Spring is still a month away
, so I've a little time left. The other ideas seem to have some merit and demonstrate the ingenuity of my fellow cyclists!