[Geek]

opelgtsource has replacement belly pans (fiberglass), if it is completely shot. Check out http://www.por15.com for all sorts of good stuff for metal. They have a kit for repairing rotted/rusted floor pans. Other than that, how are you at welding? Just remember that your better off making the hole clean of rust (even if it means making it bigger) before you start to repair it.

 

[Geek]

The absolute most important thing to have before you start any engine work on an Opel, is a set of three square drivers. These are fittings for any regular ratchet (can get in either 3/8 or 1/2), and resemble Torx wrenches. Unlike the eight pointed configuration of the Torx wrench though, these have twelve points (hence the name three square). You'll need sizes 12, 10, 8, and 6 mm for the various places they're used in the engine, and a set usally costs around $35. I got mine through a automotive tool shop, who in turn ordered them from a place called Automotive Equipment Technologies in Northern VA. These wrenches are needed when doing things like removing the head (which is held on by 10 12 mm bolts at about 110 ft/lbs). If you try to remove (or torque down) these bolts with another type of driver, you'll likely strip it.
The gaskets and other rebuild needs can all be had at opelgtsource, and sometimes come up for sale on ebay. Good luck, and let us know how you're doing.