I believe they all require the use of the ignition key/lock which defeats the object to me. This includes the latest Plus Four which further requires you operate the key against the normal starter detent spring to arm the starter button

Having said this I thought it period appropriate to have a button Start for the 1936 diesel twin on my narrowboat.
![[Linked Image]](https://i.imgur.com/O4JEaPB.jpg)
Ignition switch is simple on/off.