Hi Petey-do a thread search on "Reccessed Firewall Ideas" on here.I found a bit of helpful info. I,m in the same boat-puttin, a 289 in an early A Tudor-it,s a bit tight in the R.H side header department too!
Use a shorty water pump either from Ford Motorsports or Snow White Ltd - www.snowwhiteltd.com and you may not have to cut the firewall - it will shorten your installation length by 2". Recessing your firewall should be the last resort.... Snow White Shortie:
Take the firewall out, turn it around 180 degrees and weld it back in. Original uncut firewall recessed.
Large cake pans have a rolled edge and come in lots of shapes and sizes. Try a restaurant supply store.
I think the only pre-made ones you can buy for the 28-29 are 4" recess. The wagon and wheelborrow ideas I have seen pulled off very well, I just don't have any photos to show.
Awesome guys. Love that coupes firewall! Craftsmanship right there! Now to find a wheelbarrow with thick enough steel!