I've recently spotted a Bertin frame in a bike jumble around here. There's no info about it but the forks have Vitus decals (worn but seem to be 88 and a Durifort 831 sticker on the seat tube. I'm trying to work out if this is a high or low-end frame from the tubing. It's lugged and I'm guessing from the 60s or 70s but as I said, there was no info. Any tips to identify/age it would be appreciated