I have taken a closer look and am amazed that the motor ran for more than just a moment or two before it broke those pushrods! They are definitely non-standard and clearly NOT Vincent components and not designed to be used in a Vincent motor.
Here is a close up of the end of one of the pushrods that came out of the motor - look closely and you can see the witness marks where the shaft was hitting the surround of the cup in the cam follower!
Now here is a photo of an original Vincent pushrod ET 43. Note how the shaft of the pushrod is 'waisted' immediately above the contact ball to ensure sufficient room for it all to move as the cam follower falls and rises on the cam.
Without the 'wasting' a plain ball end push rod inserted into a cam follower cup can only 'rock' around 10 degrees because of the constraint of the cup walls. The genuine part, with the 'wasting' of the shaft is able to 'rock' around 35 degrees - this means the genuine part never makes contact with the cup walls and so is never subject to bending stress, even with a high lift camshaft.
The 'wasting' of the correct ET43 pushrod shaft is also visible in the Spare Parts List, drawing MO13.
Easy fix - fit the proper parts - DO not simply reinstall the poorly designed parts that were there earlier.
Its little things like that that make a BIG difference.