In maya I could constrain the position of one object to another with a point constraint. I found the transform constraint in houdini, but it constrains all the transforms and I only need to constrain the position.

How might I set up a position constraint in houdini?

you can specify the transforms when making the constraint
or edit the parameters in the CHOP network

So the trick is to use a blend constraint and not a transform constraint? Using the masks on the blend constraint looks like it should give me the same constraint functionality I had in maya (parent, point, rotate and scale)

yeah - I think (can't remember) that Maya's constraints do the same thing - they just have aliases for the different types:
Parent = translate, rotate, scale
Orient = rotate (but really it's a Parent constraint with T and S turned off)
Point = translate (but really it's a Parent constraint with R and S turned off)
etc

FWIW, in Maya, parent constraint doesn't constrain scale. Might be a Parent with scale disabled!