Ok, this is primarily for those who have or know about the old campy NR or Record or GS parallelogram derailleurs (from the 70s to mid 80s) vs the slant parallelogram style popularized by suntour and shimano

The reason I'm making that distinction is because based on how the two types of derailleurs work, it seems to me that the slant type would work better (or tolerate) a shorter chain length because the pulleys stay closer to the freewheel (cassette) as the different gears are selected. So, I can see how the method where you wrap the large cog in the back and the large chainring (skipping the derailleurs) and then adding a couple of rivets to get the proper length would be appropriate. Being the campy style is more vertical and therefore the pulleys naturally travel farther from the freewheel wouldn't this require an inherently longer chain?

The case in point here is I have a mid 80s CIOCC 42/53 crank w/ 13/21 6sp freewheel, the previous owner swapped out the original campy record for a late 80's dura ace. Being everything else is Italian I'm converting back to the correct record derailleur and the existing chain seems too short.

thanks
Steve