Luckily for me (and my grease gun) that was just a little light trickery on the retainer ring on the outside of the cap that made it look like another grease fitting, but I did do a doubletake and go back and look at the car. I thought I was going crazy for a minute. To address your statement on the Rear end of the car in a very long winded way;
When I purchased the car (sight unseen), we really didn't know what kind of shape it was in. I found it on a website called bringatrailer.com that linked to its ebay page. What I was most concerned about was having a clean body and at least mostly unmolested frame. What I have been looking for for quite a while is an original Ace or Aceca that was rough enough, or missing enough to warrant not only a complete restoration, but a true resto mod, bringing its performance in braking, steering, and acceleration right in line or above anything modern. The drivetrain that I wanted to put in was a new 5.0 Coyote Ford motor, with a 6 speed and Ford IRS. The goal was to use nearly all Ford components including the front and rear unequal length control arm suspension, 4 wheel disc brakes, etc. The width difference is dramatic to say the least, and custom aluminum fender flares would have to be moulded on and a considerable amount of the original body would be lost, as well as pretty much any portion of the frame that wasn't holding the body on. Needless to say, this idea is quite blasphemous to some, but what I wanted was a car that really couldnt be brought back, or one that could but would require a rebody or so much work that its originality would already be lost.
That was the plan, until we got the car. It looked like it had been driven into a garage in Southern California, had the guts pulled, started to strip the body and forgotten for 40 years. There wasnt a speck of rust (except for inside the gas tank) and the suspension and steering were not only salvageable but in fantastic shape. I had the entire body and frame soda blasted to try to find anything wrong that could justify such an aggressive modification, even getting so far as to start to mock up what would be required to get the rear subframe mounted in. I just couldnt bring myself to cut anything.
While we were debating what to do with it, I received a package in the mail. It was a forwarded package from the previous owner (from around 1971) it contained tons of hand written and typed correspondence between himself (A dentist in LA) and the AC factory, and original letters from the AC Owners club welcoming him to their community of 15 Members nationwide, with only 4 in Cali.
The fact that we knew the original motor was long gone, and that it had a V8, but that too was long gone was one of the biggest reasons why we wanted such a radical build out of it. After reading all the letters and information on it, we found out it had a Chevy 265 V8 (the first Chevy small block) sometime in the late 50's/early 60's, then was given up for a Ford 260 V8.
After reading this, it just seemed wrong and cruel to do the resto-mod, especially because I already knew a guy who had a 64' Ford 260 for sale that came with the Borg Warner 4 speed.
We changed our plans and started the build that you see now.
I wanted to keep what we had intact and build around that base as cleanly as possible. Everything about these cars is so beautiful in its simplicity, so I wanted to show off as much of that simplicity as possible. The parts that were missing, I tried to recreate using the same handcrafted look that these cars originally had, but not being afraid to stray away from the original configuration of, say, switches or type of light, hence the modern headlights, amber turn indicators and Overrider bumpers moved closer to the body.
Getting back to the rear end, prior to moving forward with the new plan, we pulled the rear diff, and inspected the guts. All of the bearings were in fantastic shape, and luckily the bearing numbers still indented on them referenced over to modern bearings, I wish I could say the same for the Girling brake parts, those part numbers go off into oblivion never to be seen again.
The 260 Ford puts out similar power to the Ruddspeed 2.6, and our goal was to not overbuild the motor for the chassis, specifically the brakes, which is why we chose not to go with a 289 or bigger. The brakes were upgraded with larger capacity Wheel cylinders and a modern master cylinder, but as you've already stated, I think heat will be a bigger enemy to the car than stopping force. but that will come down to the driver