You will need to replace the meter with a larger size.
And upgrade the water service to 1.5"
The flushometer valve will need to be 1"
I've talked to plenty of homeowners that talk their plumbers into trying this without the plumbing supply upgrades.
None of them would ever do it again, and most have them have take the flushometer style toilets out.
When you flush one of these, all the other fixtures in the home lose pressure.
You need to provide an instant 1.6 gallon surge.
This is why you have tanks in homes, it may take 35 to 120 seconds to refill a toilet. And even a slow refill like that, it will scald anyone taking a shower.
Now try a 3 second flush with your ex-wife in the shower.
That's what she will be, your new ex-wife, the first time you flush that baby while she's in the shower.
But if your still want to try, upgrade the meter to at least a 1", replace the water service to 1.5" and keep it that size until you branch to 1" for the flushometer.
Shouldn't cost you more then $5,000