Please identify these NOS 6550s

would agree with @jond , get them tested before you do anything. no point in using your amp as a tube tester. a 20 yr old Shuguang is going to be good for the trash,  likely not good for normal use......that shuguang was made back when  you had a 50/50 chance a new shuguang would go super nova on you on power up. 20 year old chinese tubes are well known for their high failure rate, especially in something that runs high B+