As a caution, your Dexta is now likely to be 'negative earth'. No biggie, just something to be aware of.
It's a question of reliability or aesthetics.
What I'm seeing are reliability type upgrades. The p3 was always a good starting engine so I would suspect when the time expired original needed replacing, a geared starter wasn't much more expense and reduces stress on other 60+ year old components. If it were mine I'd consider leaving it alone but fit a dummy lever to the dash just to look right.
I'd keep the alternator without a second thought. An alternator system doesn't need a control box. The charge rate is probably a 50% or more increase compared to a dynamo, again a reliability upgrade. But, the visual difference between alternator and dynamo is quite obvious. On the showfield, a rivet counter with a pocketfull of jam sandwiches and zero understanding of A-V-O will joyfully point out to anyone bored enought to listen that the alternator is wrong.
Most of all, remember it is
your tractor, no one elses, get out there and enjoy it.
My opinion, like others, are just opinions!

If it works, leave it alone.