Next Saturday I'm shooting a wedding as a favour. (Long story.)

The way the weather's been looking (rainy, dark and more rain) there's a strong chance I'll be shooting indoors at the venue. Being indoors will necessitate the use of flash, I strongly suspect that it will have to be on camera for various reasons, no one to assist, only 1 tripod, time constraints etc. The ceiling is too high and dark for bouncing.

I have 2 questions,

1. How effective at reducing the harshness of shadows are the metz bounce attachments? (A bracket which attaches to the flash and holds a card.) Or any other suggestions.

2.Any suggestions as to how I can effectively use flash to light a group of 80 people? I have at my disposal 2 metz 45-ct1's and a vivitar 385.