Yamaguchi made some rebadged "GT" track bikes for the US Team, they were brazed steel frames.

http://www.yamaguchibike.com/content/History

Koichi began working with the US Cycling Federation as National Team Mechanic in 1988, and, in 1989, he began making prototype frames for the US National Team and became the lone official framebuilder of the United States Olympic Cycling Team.