Once you have the opening enlarged it will bear the rough silhouette of an 8 and you can try lining the case up. There is a lip at the front near the E-module which may hang you up. Grind this down until it's out of the way. You may find that one of the bolt holes toward the rear doesn't quite work anymore now that the case is flush; just chase it with a 1/4" bit. The fifth hole- I got a Canadian tire drill 90 attachment to drill the final hole deep in the footwell. You can now secure the chaincase to the tunnel for final mockup and, using a 1/4" bit drill upwards through the bulkhead drill the 2 holes through the anchor plate.
Disassemble the two chassis cross members from the old chaincase and place them back in the chassis, securing them at their opposite ends. You will use these to determine your hole location on the top tab. Mount them in a forward location relative to where they would sit after final assembly. Remember, if this hole is wrong it will distort the clutch tower. Thread the drill bit through both eyelets positioned on the front of the tab (they will be assembled as stock on the rear afterward) and use them as a guide to drill the hole.