Well, it's tough to say, because each bike has it's own individual characteristics, but there are some basic generalities.
The main issue is that the 350 barely has enough horsepower to do those kinds of speeds, and you'll be pushing the bike at the limit for hours. That will kill it right off.
I think all it will do is about 65mph max when you're sitting up,
A general guideline for extended riding would be about 75% of maximum speed on a Bullet, which would be about 48-50mph on a Bullet 350.
Even the 500 should only cruise at about 60 mph max for extended periods.
The fastest way to get into problems with a Bullet, is to try to make it a highway bike.
It will never be one. Especially a 350 Bullet.
This is not a modern bike or a big road bike. It's an ancient commuter bike, designed from a time when there were no highways and all speed limits were around 45mph.
If you really want to use this bike for longer distance, find a B Road route to get there, don't do over 50 mph, and leave earlier so you can get there on time.
That would be the best advice.
If you want to test your luck at 55 mph or more, then I'd recommend slowing down to below 50mph about every 5-10 minutes for cooling purposes. You don't have to stop totally. Just a slow down to the speeds that you "should have been riding at previously" will get you by. You should allow sufficient time for the engine to resume normal operating temps while running slower. Say about 15 minutes at the slower speed before attempting to resume 55 or more.
And mind you, this might not work and you could find yourself with a seized engine on the side of the road, waiting for a tow truck. It has happened to thousands of people before you, who contemplated trying it.
I'm not trying to throw a "wet blanket" on this, but every one of us here has had to accept the fact that we don't have a highway bike. And we have 500cc Bullets.