Constraint to center of profile

[80083r]

New week, new question. I've searched here, and the whole internet (it took a while, but I read the whole thing <grin>).

I have a body - for the sake of the argument, it's a square, 1" deep. I have another shape, that is a right angle triangle with the hypoteneuse being a curve, and holes cut in the centre.

I want to constrain the triangle centred in the square, so that if the design of the "triangle" changes, it will remain centred in the assembly.

Any ideas? I can't seem to find a way to make a work point located in the centre of either body - I can make work points and axes - but the centre of the "triangle" part is in empty space.

[MarkWink]

...I like to hide a very small hole with odd shaped parts, so it allows for something to constrain to