Now what do I do about those huge *** holes in the firewall?

 

same thing ex-police car owners do, fill the holes up so they don't leak when it rains.

if you've got any radio shops in your area, there is a good chance they will have rubber plugs that will fill the holes. if not some, you can rivet or weld some metal to close the holes.

 

I made some steel plates, and screwed them onto the firewall. Here is a pic. Not very close though.

 

Well, that is a little small, but you could imagine how to make them.

 

I had sheetmetal welded into my firewall where the blower unit was. My car is also right hand drive, and I have the steering column on that side also.