Originally Posted by The MAX

So as seen in my post here, I just got an old Colnago Sport to do up.

I was looking to get either a Shimano 600 or a Shimano 105 derailleur set with downtube shifters, but the 7 speed indexed shifters seem to be not very common.
Shimano 105 and 600 7-sp index levers are very common on eBay.

First of all, will the Ultegra 600 (tricolor era) RD work for 7 and 8 speed?
Yes

Same for the 105 of the same era?
I don't know, probably.

I know, however, a 8 speed shifter won't work great for 7 speed.
Works just fine. Spacing is almost identical.

Should I go 7 or 8 speed?
Depends on what you want to spend. 8-sp will require a wheel change.
I'll avoid the 8-sp freewheel discussion because I know nothing about them.

7 seems easiest due to not having to alter the frame spacing, but 8 speed parts seem to be easier to come by on ebay.
Add a 7-sp freewheel and 7/8-sp RD/FD/Shifters for less than $100, and you should be fine if that's what you prefer.

Add a 7-sp freewheel and 7/8-sp RD/FD/STI shifters for about $200, and you should be fine if that's what you prefer.

Add an 8/9/10 wheelset, cassette and 8/9/10 RD/FD/crankset/bb/Shifters for about $400-$500, and you should be fine if that's what you prefer.

Get a donor bike, swap over the newer components, build it up. Swap the old stuff back to the donor bike and sell it to offset costs, if that's what you prefer.

The main thing is how you want to ride, what you want to spend, and how far you want to take it.

If anyone has any of these parts let me know. I've got the original modolo brakes and levers, as well as Gipiemme downtube friction shifters and front derailleur, and a Suntour rear derailleur. I know all of it is not real desirable, but I've also got $$$, so just let me know if you have some Ultegra 600 or 105 RD, FD, or shifters you wouldn't mind parting with.
This part is for the ISO/Trade thread. Make your decision first, then go there for parts.