The new A/C compressors from Sanden are made to be used with R-134a so this should not be a problem.  I have these new for $329 with no core charge.  I would also recommend replacing the dryer as it may be contaminated and is only an extra $60. Also I would replace the expansion valve, as the new ones are set up for the higer pressures of R134a and these are $30.  You can give me a call and order this stuff or buy it through the webstore.  However no matter where you get it, these are the items that I would recommed replacing when you replace the compressor.

Thanks,
Ken Wilford  (Licenced A/C Tech, Certifiable Vanagon Nut, etc...)
John 3:16
www.vanagain.com
Phone: (856)-765-1583
Fax: (856)-327-2242