A lot of people bolt the crossmember through the floor, that works ok, if you make up and fit strengthening plates to the floor area where you bolt it though.
I made plates up from the top, with weld in captive bolts, and plates on the underside.
This was on a MK2 Escort, but the idea is the same. I think my crossmember is a Sierra one.
Check out my Johnnys Escort sport build , its on there.