Get something to diffuse your flash (softbox, handkerchief, whatever) and take and develop some practice shots, using the auto-exposure function on the flash, quick! Be sure to include some bounce flash when you do.
Also, take some using the flash on manual, using your flash meter.
Be sure to use the film you intend to use and the lens(es) you intend to use for the wedding, and then develop using your standard procedure (if you have a variety of standard procedures, I'd lean to smooth tonality and moderate contrast).
Check your negatives to see if the auto function results in good exposure. Check as well that the flash meter is accurate (for your camera, film and development).
Here are some pre-wedding suggestions of things to check.
If your flash uses AA batteries, get lots.
Check to make sure that the flash sensor is clean and unobstructed. Check to make sure that the flashhead lens is clean and unobstructed.
Make sure that the battery contacts are clean and make good contact. Make sure that the battery holder clicks in positively, and stays in - take some duct tape too!
Make sure that your synch cord is in good shape, and makes good contact at either end. If at all possible, get a backup for the cord.
If at all possible, take along a backup for the flash. Even if it hasn't nearly the power or flexibility, a second flash that works is infinitely better than a first flash that is broken.
Flashes can yield a very satisfying learning experience when "dry fired". You can familiarize yourself with the adjustments and controls, without wasting film. If you can and do use rechargeable batteries, it is almost cost free.
If your flash can use both rechargeable and non-rechargeable batteries, take both.
If you have a PC tip conditioner, use it, and take it with you.
Bounce flash works great - especially with just a little bit of reflector peeping over the top, to give catchlights.
Try to have the flashhead above the lens, rather than to the side, whenever possible.
Don't forget that reflectors can be used effectively with single flashes. Don't forget that window light can be great in weddings as well.
Your RB67 lenses will synch at any speed. If by chance you also use a camera with a focal plane shutter, remember to set the right speed.
This is a comment about the RB67 lenses - I don't have one. Some shutters (such as those in the Mamiya C series TLR lenses that I have) give you a choice as to which flash synch to use. If yours do, be sure that they are set to X (not FP).
Now that I have given you a million things to think about, it would only be fair to provide some reassurance.
I have 4 working Metz flashes that I have used for wedding work. I have used others as well. Metz makes very good flashes, that give good quality light on a repeatable basis. If working properly, they are well suited to wedding work, and in my experience they are rugged and reliable as well.
Good luck.
Matt