As a follow-up:

There are many possibilities for finding a Picatinny rail blank to fit to your dovetail. Many blank rails are available from various outlets. Here's one from Amazon:

http://www.amazon.com/Sports-12X0-40-Inc...=picatinny+rail

Like most, it is aluminum. You might want steel. There are steel blanks available as well.

Here's a whole selection:

http://www.amazon.com/s/ref=nb_sb_noss_1...+bla%2Csporting

Curl