this isn't it, but
they may be able to advise you.
their ad is oriented toward old professional videotape formats.
415-821-7500 fax 415-821-3539 (San Francisco area code)
Also look in your yellow pages under tape duplication. Might get some advice there. If the tape is in really bad condition don't trust no yokel, and don't try to be too cheap.
I wonder if library of congress might advise? web site or phone.