Any topping lift for this boom needs to be able to lower it to the deck or rail or pull it well up above. Those so-called 'topping lifts' of about 24" long that hold the boom to the backstay, or the staysail boom to the mast, are essentially useless as a 'topping lift' - that's just a means of storing it 'out of the way' (a term I cannot abide on a sailboat. It's not in the way; it's part of the rigging. That's like saying your car's transmission is 'in the way').
If you can't get the staysail boom out of the way, it effectively cuts the deck in half. You've got to climb over (only when furled, and dangerous), go around ahead of it (long trip on narrowest part of boat), or duck under (ow!). I've dealt with this on Cherubini 44s for years, to the point where I would rig any inner staysail with either a detachable boom or none at all. In fact a lot can be said that the boat will trim better with a loose-footed inner staysail (even one on its own roller-furler). Try it and see
So in short I'm saying to not look for a piece of hardware to fasten the boom to the mast. You shouldn't want to. The only reason I see for such hardware is for when using the staysail boom as a ridgepole for an awning or winter cover; in which case you can lash it to the spinnaker-pole eye on the mast (which is normally set, or able to be moved to, right opposite the main boom, making a very practical profile for any such cover).
