Crashbox to synchronized conversion?

I should add that the conversion would be fully reversible, such that the original gears could be refitted in the future if desired.

 

For clarity the transmission shots in posts #12 and #20 are from the Ferrari five speed limited slip transaxle as used in the 1954 F1 553, the 1955 500 Mondial S2 and the 1955 750 Monza.

 

Which should always be considerable part of the objective if/when customizing/modifying any and especially historically important vintage car(s).

While not transmission related, I'm currently dealing with a headache caused by someone having converted a quite rare (non-Ferrari) distributor to Pertronix and thrown the original breaker plate assembly & vacuum advance unit away. This is over 60 year old OEM high-performance distributor used in two years and in quite rare car/engine model only.
We just want to restore it back to "just-like-it-came-from-the-factory".

 

A casting of the original casing can be made and the new synchromesh gears could be installed within. However, I would not mess with it and keep it all original. It would be important to me to use the car how it was built to get the full authentic experience of using/enjoying the car.