Guys, thought I would share some learnings for those doing this swap. I recently swapped a C4 out for a TKO 600 in a 1969 cougar with a 408 stroker. First problem was when the trans arrived it was locked up. A call to MD and they told me how to fix it (seems this is a common problem due to shipping) . Second problem and this is the one that really tics me off is issues with the hydraulic clutch setup. I installed the one with external slave and had a heck of a time bleeding it. Once bleed it would not move enough to disengage the clutch! So a call to MD and they tell me I need to pull the trans and shim the ball stud for the clutch fork out. So will pull the trans this weekend and see if that fixes the issue. There tech support is great but there instruction leave a lot to be desired.
Ray, I have the exact same setup and haven’t had any trouble with clutch disengagement. I do know from other forums and speaking with their tech support that they switched from a .70 bore master to a .75 bore master to move more fluid and get enough stroke on the slave.
I’d check the bore size on your master and talk to them again before pulling the transmission.
I have that setup on my '70 with T5 trans. No issues.
There’s a lot of moving parts on the linkage inside the car as you know. Adjustments there can make a big difference too.
I didn’t have any of your issues installing my TKO6 from MD with the external slave. I set everything up out side the car and had the linkage all set and made sure there was enough travel before the install. I remember having to change the pivot ball on the clutch fork to get the right travel on the linkage. The only issue I had was I had them modify the shifting rails for smoother shifts with the Kevlar pads and 5.0 shifter. They took a used cover and rails and modified them instead of modifying new parts. No dice 
they had me return the trans and they shipped another one. With the shipping cost I’m sure they lost money on that sale.
Once you get it broke in change out the Amsoil and go to the GM fluid. Shifts smoother with the GM fluid.
No issues installing my MD linkage to the Toploader, or when I swapped in the T5.
One tip on filling/bleeding…use one of those hand-pump oil cans to pump the fluid in from the slave up to the master then to the reservoir. Worked like a champ.
Thanks guys for the info. The linkage under the dash is correct but according to MD the clutch fork is not in the right spot. I am using a T-5 bellhousing and the clutch fork as it sits is dead center in the opening when it should be closer to around 25 percent from the rear of the opening. Going to shim the ball stud with a flat and lock washer to get it there.
When I did my swap I used Modern Driveline’s cable linkage and I like it. I know this is of no help with this, but for others in the future to see and consider.
Here is a pic of mine. The marks are spaced the distance MD specifies the fork should travel.
They are definitely still shipping out the 0.7 master cylinder but should be OK if you are getting the full 1.4" of master cylinder travel. I am in the middle of my FMX to TKO600 install now on a 68, yes it’s a FMX that someone installed at some point. I couldn’t get enough master cylinder travel in mine (1.1" MC travel) so I am getting a larger diameter master cylinder free of charge including shipping. All in all though, definitely a good product and good customer service, glad I got the full “kit” as I have had no issues outside of pedal travel during any of the install. Drives nice too.
Ok thought I would provide an update. Pulled trans and bellhousing, added a couple of flat washers to shim ball stud out and put everything back in. Bleed the hydraulic clutch and everything is now working 
.
Glad to hear you got it worked out. I bought the full kit from them. Everything has been great and their service is fantastic.
On a related note, I’m using the Scott drake leather boot and I didn’t feel that it was enough of a barrier between the interior and the elements, fumes, heat, road noise…
So I made this - a flat piece of heavy rubber cut to match the shifter boot base with a hole cut for the shifter, and cut a small cv joint boot in half and glued it to the rubber. Basically it’s a mini shift boot that goes between the floor and the carpet.
What # Hurst stick did you use, I need one.
I need to make one of those inner boots.
That is a very cool modification. The only thing I would add is a bit of bailing wire around the opening where the shift lever comes through the round opening, to close that off. It won’t be seen but it should keep the fumes under the car.
I didn’t take a picture of it, but I used a large heavy duty zip tie to cinch off the opening around the shifter.
If I was to do it again, I would have wrapped the shift lever in tape or used some rubber to increase it’s diameter and not have to cinch down the opening on the boot as much.
Slick solution. The 5.0 Mustangs use a similar looking lower boot too. It is available repro for a few bucks and might be a good solution for the next guy to make the swap.