The Midwest Plan Service publishes a Structures and Environment Handbook which address gussets in section 406.5 under Wood Truss Design. The most recent edition is a 1987 Revised 11th Edition.
Midwest Plan Service
122 Davidson Hall
Iowa State University
Ames, IA 50011-3080
Toll Free: (800) 562-3618
Customer Service: (515) 294-4337
Fax: (515) 294-9589
E-mail: mwps@iastate.edu
Other info available at https://www-mwps.sws.iastate.edu/