I have a 64 Cyclone that based on the ROT sheet came with HIPO engine. It does have the export brace from the Firewall to the shock towers. When I did the restoration I did not see any extra washers at the shock tower, but the brace is bolted and spot welded from underneat at the firewall. I would like to see some pictures of what the Mustangs look like to compare with.
Rick