I've seen the number for 1998 S70 T5M's on this site (361, IIRC), but never for V70's. I placed a few calls to Volvo Cars North America recently (due to my example being hit and totaled). Their sales planning department found the following figure (not guaranteed to be exact, but it's what their records show):
1998 V70 T5M's imported to US: 127
Then take away at least four that I know to have been totaled, and there you go.