I opened your assembly but only in design review mode due to not having any of the parts/sub-assemblies.
Not knowing how you created this I can only answer based on assumptions.
I would do this in three main steps - In your assembly you need to create an angled plane so that you can mate the centre assembly to it . This can be done in your existing asssembly
1) Firstly create a sketch - sorry it's in metric but you'll get the gist...this sketch can define the leg height at each end and a driven dimension for the angle (or make it driving).
2) Add an axis - Exit the sketch and select a point and a plane perpendicular to the intended axis (I used the default FRONT- using Insert> Reference geometry
(how to insert reference geometry)
3) Now add a plane using Insert> Reference Geometry, but this time, select the axis and the line.
The final result with sketch, axis and plane showing
From there you can add mates to it. I created the assembly in 2015 - ping me if you need it and I'll send you the file
thanks you sooooo much for your reply Alex, that was great. i have the 2014-2015 version currrently. if you could send me the file that would be great. maybe save it as an earlier version ?
let me attach all the parts here so you can open the whole project if you want. maybe that will change your approach or what not.
again, thank you sooo much for your time.