The VersaMil manual calls out a Morse taper spindle, but not the number.
If you can sell the machine to some collector or person who needs the portability of the Versa Mill for enough money to buy what you want that's lovely. Otherwise, machines are just another consumable in a working shop, just the service life is hopefully long than for an end mill
Converting a useless piece of obsolete stuff into something useful is a fine thing. Most old unusable machines are in reality only worth a few dollars per hundred pounds at the scrap yard, or perhaps suited for a "Rustoleum rebuild" to decorate some corporate lobby or steam punk fans residence. Hopefully a working and functional VersaMil would be worth more, but how much more I don't know.
The biggest thing is not letting the lumps look close enough to what you want that you invest a lot of time and money but still end up with clapped out bits and pieces so the end result is less than satisfactory. I bet many here have gone down that path, my exercise was an old pre WWII SB13. It was mediocre new and 70 years of use and neglect had not made it any better.
VersaMill is apparently still in business, so there must be a need for their machines. You might be able to get some bits and pieces to make it more useful without major modification, or some ideas for accessories to make it more useful. URL is versamil.com - note the single "l" in the URL. An XY table on a base made to allow the VersaMil to be mounted in more than one position or the table to be swung 90 degrees would allow mounting lathe tools on the table for turning work and also using the XY table as a more conventional mill table.
On the occasion someone has wanted to tell me it's terrible to modify some "classic" bit of gear I've always asked if they are willing to buy it for the value of what I'll end up with after the conversion is done. Never had any takers, funny how the put the money up to match your superior world view approach shuts down those who want to tell everyone else what they should do.
The machine you have beats the machine you wish you had when it's time to make things happen, took me a while to start making parts instead of excuses.
I'm guessing in New Zealand the cost of new machines with shipping is significantly higher than here in the US. Using what you have to get what you want can be a good option if there aren't many buyers to help fund a machine that better fits your needs.