I am building a fixed/free conversion using a Trek frame. I got a set of wheels (Formula hubs w/ Mavic CXP rims) and have a question regarding which cranks would work best and why.

I have:

1. Early 70's Campagnolo road double crankset (172.5mm) w/ same era campy BB, headset and matching bakes & non-aero-levers.

2. Late 80's Shimano 600 road double crankset (165mm) shimano BB, head set w/ modern Shimano long reach Dual pivot brakes and non-aero levers.

I am thinking gearing would be 42x16 (fixed and free) and was wondering if one group would make an easier build regarding chainline etc. over the other? Bars will be road drops of some kind. Below is a pic of the frame when it was built up as my commuter. I got another geared bike for that and then got "downsized" so I want to try somethiing different to keep riding fun and interesting while I am not working. Comments and advice are appreciated.

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You're going to want your chainring to be 42mm from the center of the seat tube, give or take a mm. If it's off by 3-4mm you can compensate by using a 1/8" chain. If it's off by more than that you'll need to either move the chainring to the other side of the spider, get a different size BB spindle, or both.
I would opt for the Shimano group as the cranks are shorter, and 165mm cranks with a 42x16 ratio sounds perfect, especially if you have some hills in your area.

For looks the Campagnolo set all the way.

However, 165mm cranks are much more fun on a fixed gear than 172.5, esp. on a conversion (lower bottom bracket). Shorter cranks mean easier spinning. Check Sheldon Brown's article. So I'd tend to go for the Shimano. The chainline will be dependent on the length of the bottom bracket and whether you use the inner or outer chainring. Usually the inside ring of a road double (any road double) is pretty darn close. There are definitely exceptions but more often than not this works out okay.

Headset, Campagnolo all the way. Buttery.

Brakes, tough one. In my limited experience with them, I have found 70s Campagnolo brakes (GS & NR) to be more than adequate. And they look great! But I know that people with much more experience than I rate the late 80s Shimano 105 as the best sidepull brake ever!! Does this mean that the 600 of that era would be almost as good, I don't know. Your choice.

PS Looks like it'll be a real nice bike!!! Good luck!!

I really wish you wouldn't convert that. It looks downright gorgeous, especially with the moustache bars and bar-ends. Why turn the perfect touring rig into a so-so fixie?

I agree don't screw with that bike. If want to make the ride interesting by having only one gear, then just don't shift. It'll be even more fun because you'll have to resist the urge to shift.

I understand that sentiment but I already have 2 geared touring bikes. 1972 Chrome Schwinn Paramount and a 2007 SOMA Double Cross set up as a commuter. I would not do anything to the frame, like cut of cable guides or deraileur hangers and it could be built back up in a couple of hours. As it stands right now a lot of the parts in the pic were swapped over to the SOMA. The SOMA was able to take 35mm studded tires for winter and the Trek (710 1981) had a max of 32mm w/ fenders. Also I am not kidding myself that it is going to be like a true track bike, just a fun way to do somethign different than I am currently.

My White Ind freewheel cog on the Formula hub produces a chainline of about 45mm which is a perfect match for my Campy Super Record road crank with chain ring mounted on the outside.

boo glenside.
glenside kids think they're champagne... but they're not.

I'm 40.

that's okay. glenside is still not as cool as paoli.

Funny you say that because I sold my house and am looking for house in Paoli. My wife wants to be closer to her parents in Devon.