I can't help with the post size but what the OP has is a 1991 model. According to my literature, in 1990 it just the Boulder with Shimano Deore LX. In 1991 it they added the ATX designation and spec'd it with Sun Tour X-1. It was replaced by the Sedona ATX for 1992. The serial number should confirm this and provide the manufacturing date, down to the fortnight. X-1 was 7 speed in 1991.
Last edited by T-Mar; 02-23-19 at 08:16 AM.