I am buying a late 80's Yamaguchi made steel frame from his Proteus days in Maryland. It is an awesome bike but I would like to use an sti system on it. What is involved with converting. Will i need a new wheel, cassette and deraileur? Tell me the best way to do this. I will be keeping all the original parts.
 the search is not working. already tried that.
The shifters, cassette, and chain need to match, all 9-speed or 10-speed. 10-speed would be preferable because replacement parts will be around much longer and the extra cog is nice. The old crankset/chainring set may work fine, at least if they are in good condition they would be worth a try. I don't believe the 6-speed D-A rear derailleur will work because of the throw ratio.
9-speed and 10-speed cassettes will fit 8, 9, and 10-speed Shimano compatible rear hubs. You will need a new rear hub. Depending on the value and condition of the old wheel rims and spokes you may want to rebuild both wheels with new rims and new spokes, or you could just rebuild the rear wheel with a new hub. The steel frame can be spread to accept the new hub with 130mm dropout spacing.
I don't know how important it is to you to convert to STI. If the old components are in good condition I would probably clean and lubricate all of the bearings and ride it as is.
Thanks for the info. I should be picking it up tomorrow night. I'll measure the spacing then. I adjusted the components when i tested the bike and the front derailure worked well and the rear worked really well. I was just tossing the idead of STI around. Something about new stuff on a nice old frame. Also to cut a little weight.
Not trying to convince you one way or another but I think you would add weight by converting to STI due to the shifters' weight. 6-speed D-A should be pretty light.
I refurbished a 1980 Trek that was equipped with Shimano 600 6-speed freewheel. The drivetrain was so smooth I elected to leave it alone. Instead I cleaned and lubricated everything that moved and rebuilt the wheels with new rims and spokes. Great riding old bike.