Sorry to follow up my own somewhat hasty post...

The fan I used is intended to mount with soft plastic screws that run through the radiator core and have plastic nuts on the other side. This is a 12" fan, and there is just barely clearance for the rotating part in the radiator opening - locating it precisely is required, and the support must go horizontally.

That would work fine for most radiators, but Volvo radiators have denser-than-normal cores. I did not want to try to drill holes or otherwise enlarge the space between the fins to let the bolts slip through, so I mounted the fan to the body using small angle brackets, and with the support vertical.

This created a clearance issue with the front edge of the hood when open (the hood was off the car when I mounted the fan, duh...). Even with relocating the thermostat control from the fan support to another location, I had to drill the top hole in the hood support strut 1" lower in order for the hood not to hit the support. The hood therefore latches slightly less open than before, although it's not really noticeable.

If you do choose to go through the core with the screws, you won't have that problem. (No, there's no room for it to go on the other side of the radiator.)