I have to ask, what vintage and model Raleigh? You might want to convert to
standard bolts as you can't readily convert the rear bridge of the frame to
match, and you might find someone willing to swap you the part you need. If
it's a bike that is at all collectible, I would hesitate to partially convert
it for the convenience of using parts in hand as you diminish the "value".
What kind and model of brakes are you using? If your brakes are Campy and the
reach is right (a lot of older Raleighs used long reach brakes, some even
needed a drop bolt on the rear), you can use your front brake on the back,
and you only need to buy the longer front bolt to convert your other brake to
a front. If you have some other modern short reach brake, make sure they fit
before you go drilling crowns. A proper set of brakes appropriate to the
vintage of the frame should be easy to find if you wish to keep the bike
"correct". Convert carefully, not hastily.
Stevan Thomas
Alameda, CA