I have a 1987 Bianchi Trofeo... and at the moment, I have an Ofmega crank set and bottom bracket. The drive side crank arm appears to be showing the first signs of some questionable wear/crack marks. I want to replace the crank and probably the bottom bracket. The rest of the bike is set up with various Campagnolo parts, so I'd like to replace the Ofmega stuff with Campy stuff.

I've located a NOS 1985 Campagnolo Victory crank set that I'd love to use on the bike, but I'm not sure what to do about the bottom bracket. According to my research I need a 109 mm symmetrical Italian threaded bottom bracket. I think I might have found one on ebay, but I'm curious if there's a modern bottom bracket that I could substitute. I was told that I could probably use a modern 111 mm symmetrical cartridge bottom bracket... but I'd like further information if anyone's got any suggestions or thoughts etc etc... thanks for your help.

is the taper of the BB spindle the same as the taper of the victory crank? if so try it out.

I've been running an ofmega mistral BB with a sugino crank on a mid 80's cannondale for 20+ years and many miles with no problem. chainrings are centered with respect to freewheel. the tapers are probably difn't, and my left crank arm is probably 0.671 mm out too far but it works for me. BB is still runs smoothly.

From Brandford Bike's website (www.branfordbike.com)
Shimano and almost every major bottom bracket maker have traditionally used the same spindle end cross section of 12.9 mm and two degree taper. Campagnolo uses the same two degree taper but has a smaller starting cross section of 12.7 mm.
A Shimano crank arm will bottom out on Campagnolo spindle. A Campagnolo crank arm will not draw far enough onto a Shimano spindle.
I have seen where someone forced a Campagnolo crank arm on to a Shimano-pattern square taper bottom bracket. I thought the extractor threads were going to strip as I was trying to extract that crank with a Park crank extractor, not to mention that I could not get the extractor lever arm to actually move until I started tapping it with a rubber mallet! I wonder how they got the fixing bolts on so tight without snapping them right off?

I do not know which standard Ofmega went with so I would not be able to tell you if the two are compatible but I will say that you should be able to use that 111mm symmetrical bottom bracket without any issues. Just grease up the tapers and tighten the crank arms on to the bottom bracket with a few extra turns on the fixing bolts to seat them a little deeper.

About 20 years ago, I special ordered a campy road triple crankset [before they were commonly available] and used a shimano MTB bottom braket without any problems. The tapers were slightly differnent, but it caused no problems

I've also got a chorus crank from about 88 on a dura ace 7401 BB. No problems like squidward mentions. Bunch of frankenbikes here. Water got into the chorus BB and pitted the races, didn't have money at the time to buy new campy BB so I threw on the D.A. which I had laying around. Granted the crank arms are not exactly in the perfect locations but the chainrings line up and the arms aren't that noticeably off. The drive side crank is close to the frame but I've got a 12-19 and a 42-53 so the chain alignment works quite well for the gearing I am using the vast majority of the time (I'm slow and really shouldn't be riding this gearing but oh well).

can't help too much w/ the compatibility question, but can advise you to throw out the Ofmega crank, I had one snap during a sprint and I hit the frame so hard I bent it....found out later that they were known to be weak.

not this one. 23 years and many miles and sprints later and still going strong.

Wow that's frakken awful. I all ready ordered the NOS Triomphe crank set... not going to ride the bike till I lose the Ofmega stuff... I'd kill myself if I destroyed my Bianchi, because the crank snapped off.

Sheldon Brown has an article on square taper bb's. Campy, along with most European, and Japanese NJS, follow the ISO standard. Japanese, other than NJS, follow the JIS standard, which has the same taper angle but is "shorter and blunter."
Older Ofmega are even longer and skinnier than ISO. Nothing there about how old old is. If you are satisfied with the bb, you could try the new cranks on it and see how the chain line is.

http://www.sheldonbrown.com/bbtaper.html

He also says you can mix standards, but I'll leave it to him to explain how to get the right chain line.

not this one. 23 years and many miles and sprints later and still going strong.

One of the sexiest cranks ever made! Wanted one back in the 80's!