When did Colnago start with the straight bladed steel forks?

I'm trying to determine the date of a Colnago frame I have. If anyone can
shed light on it I'd appreciate it. It has been repainted so no model name
is on it. It has Gilco shaped tubing, Colnago cast BB shell with a club
cut-out, a web between the two chainstay sockets. Campagnolo horizontal
drop-outs, chrome right chainstay. Two bottle bosses, internal rear brake
cable routing, Straight chrome fork, threaded 1" of course, that looks as
though it was originally painted except for the tips. The parts were a
mish-mash, but the oldest parts were 1991 Shimano 600 HS and brakes.

I was thinking maybe it was a ~'90 Master or Olympic?

If anyone would like to see a pic or two if they think it'd help them narrow
it down, I'll have some pics soon.

Thanks for any help.

David
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David Bilenkey
Ottawa, Ontario, Canada