You can get the IR with only a VOR/LOC/ILS receiver. That's basically what I did 30 years ago. (OK, I had ADF too, which is virtually useless now for real-life approaches in the CONUS.) But why? If you are actually going to use your IR rating, I would recommend training the way you are going to use the rating, which these days is very GPS-centric. VOR approaches are becoming rarer and rarer, and the VIctor Airway system is being rapidly pared down to a bare minimum. Many non-metro airports are now served only by GPS approaches. Don't underestimate the acclimation factor to managing a complex navigation box and maybe an autopilot in addition to tending to IFR piloting tasks. Of course, one should be able to navigate IFR using basic equipment (especially in an emergency), but 99% of the time IFR for me is getting from A to B using WAAS GPS and flying LPV approaches to non-metro airports, and ILS or LPV at metro airports. Victor Airway navigation is so 1990s now.