the seat\tank unit is very similar to the gollner unit, as for fitting the ali tank NO it doesn't use any of the existing rubber fitting, just drill and tap it straight onto the top tube then space it up with rubber washers.
the fibreglass cover is held on at the front by the petrol cap, the cap is a screw type Yommee product bought from all good trials shops, it screws directly onto the ali tank
hope this is of help Booma
PS the bike is going up for sale, somebody is looking at it Sat 13/11, I will let you know the outcome