Direct Sheetmetal's 49-51 Ford, Mercury or Woodie Firewalls and firewall cover are available here. The small block ford and woodie firewall has a 3" setback. The big block ford and woodie firewalls have a 4" setback.
Direct Sheetmetal firewalls are made from 16 and 18 gauge, cold-rolled steel and are all hand-formed in their shop.
The Mercury Firewall is available with a 4" setback or can be made with any width or depth recess. Add info to the comments section of your order.