Just did this today. My long rod had new plastic ends and the short rod the original ones.
I ordered 4 of the metal end links from Centerline and I'm glad I did.
I started with the short rod. And yes, I couldn't make it short enough with the metal ends. They're not threaded as deeply as the plastic ones.
No big deal. I calculated that I should shorten each end of the short rod by about 1/4".
Easy. Leave the nut on the rod. Cut off 1/4" of thread on each end. Dress the cut end and put a good lube on it. Run the nut out to the end and past a few times until you can run it all the way off and start it again.
Install the metal ends and set the rod to length. Lock down the nuts to the end links.
On my long rod, it was not necessary to shorten the rod to use the metal end links. Center to center it measured 11 3/4".
But, be aware of my other findings!!!!
The used plastic end links on the short rod had some slop as did the new plastic end links on the long rod. And not just a little!! The metal end links have NO SLOP.
My car has never run better. Plastic ends may be okay for carbureted cars but with Spica, I would use nothing but metal.
It's Giuseppe's giubos, not Guido's guibos, on my 78 Alfas
REFRESH CONNECTIONS BEFORE REPLACING COMPONENTS