Karen, if the "drooling" smiliy was still available, I would be using it
Eric that was a HS50 longblock made to work with with early HS40 ignition and shrouds.
The brackets on it were from a Late model Chrome kit so it had the elongated holes that fit all small frame models. They never actually used that half tank on anything larger than H35 so the Original bracket on yours probably does not have elongated holes to fit all the small frames....They also did not make a larger bolt pattern head till mid 1969 either so if the tank is from the 60's the bracket holes weren't elongated to fit the mid1969-up HS engines.
Can just use a later tank mount on it, Just remember that the upper Rivenuts in those steel tanks are not Sealed, so be careful removing the bolts (maybe derust/decrud the inside of the tank first if needed) and when you reinstall, seal the threads good so it won't leak or seep.