Hi, can you please help to id this frame? I've found very similar one here "Basso Rocky Mountain" (https://tinyurl.com/2p8arwhk) with canti brake studs probably from beginning of 90's. So could this be some older version from late 80's or the name of this one was different (I could only find "54" mark on bottom shell which is kind of surprising for me as I thought that Basso SN from 80's were 6 digits long..)? Thanks in advance for any hint.