So Yes, it's possible to add bolts. A number of TR racers have added 4 more but it looks awfully tight on the crank end with all those holes in it!! I really did not want to drop the crank, and you need a line-bore tool to do this properly.
We finished the work - there was one snapped bolt - it was split right at the shoulder of the head. It appears that the guy who did the engine 4 years ago re-installed the existing factory OEM bolts - not even replacements! - because the bolt heads still had the British markings on them - BS for "British Standard" the way we used to have "SAE" for Society of Automotive Engineers.
We used that Fidanza flywheel, a LUK Porsche aluminum clutch, the constant-velocity throwout bearing, and held it all together with ARP hardware. I weighed what we put into it in new parts - 24.5 pounds. What came out weighed 49 pounds! Heel-toe will be troublesome for a while.
So the shifting is like cream cheese! it's smooth and precise in a way I've never experienced the TR. Also, it's no longer 35 pounds of pressure!
BUT that did not eliminate the vibration, so we're back at it. The only part of the drivetrain we have not replaced in the rebuild is the diff. It's the 1972 factory box. Since the vibration is MPH-associated rather than RPM-associated, I've torn down the entire drive train looking for the culprit. All the U-joints are new and were fine, the suspension is locked correctly, the IRS axle bearings are fine, no run out, etc.
This weekend we are installing a Nissan 200-unit diff, same gearing 3:69. Dick Good (great TR racer and parts guy) makes a beautiful kit
http://www.goodparts.com/shop/index.php?categoryID=16
I hate being in the "throw parts at it" mode.
Tom, I didn't realize your Miata has 230hp! No wonder you were on the "power" line!! That thing must fly!
I'll take the Atom. If not, The MSM.
)