Hi Allan,
Thank you for your much valued response. I apologize for my ignorance on nautical terms. I was never a sailor and this is only my third historical ship build.'
I was referring to the lower mizzen cross jack. The plans do show the foreside braces anchored through a block attached to the main mast shrouds and then attached to cleats below.
The photo on the box also shows a second set of braces from the cross jack tips running aft and secured to the aft belaying pins. This is the bracing not shown on the plans themselves.
Without these aft braces, the cross jack is pulled away from the mast by the fore braces. This ship does not have either parrels or trusses on any yards that would hold them to the masts.