Joined: Jan 2010
Posts: 9,781
Likes: 1,750
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
Also, good luck finding an appropriate high-strength longer bolt for dual-pivot calipers. Most require special bolts to say the least.
If you use the front caliper on the rear, it will fit as the old one.
BE SURE TO REVERSE ANY SLIDE-IN BRAKE PADS OR ELSE THEY'LL SLIDE OUT!
The rear caliper can then be fitted up front by using a nut inside the fork steerer tube. Add washers as necessary to achieve the right bolt length, a very minor adjustment, and be sure to get the nut tight. An allen nut from a V-brake pad will allow tightening by putting a 5mm allen key thru the existing hole on the beck of your fork crown. Again, use washers as needed for a good fit so the nut isn't bottoming out on the end of the bolt and has several turns of thread engagement.
Again, you'll need to have the pads facing in the proper direction!
I recommend the longer calipers per FastJake.