If you snapped the bolt, you won't need a tap unless you destroy the threads getting the bolt out or you cross threaded it.
The internal engine bolts can be surprisingly easy to remove when they snap, as they work in a well lubed oil bath all their lives. If you don't already have them, get yourself a couple of reverse drill bits (Grainger had a nice little kit with small bits and extractors together) and drill it out starting with the smallest bit. Center the bit well and work slow and deliberately and no thread damage should take place.
Based on previous experiences (not on a CX) with aluminum blocks and steel bolts, I've never had one that didn't come out with the reverse drill bit alone. A good dose of some freezing penetrating oil before/while drilling won't hurt either.
