91 Lumina sudden death

My wife's lumina (91, 3.1) died suddenly today.

She was driving 90 miles from a friends place, and said at first it started making a tapping noise (my kids said it was like 'perry the platypus) , although it went away when she hit top gear at about 50mph on the interstate, and came back if she went faster.

about two miles from home, she heard a weird noise, and the engine cut out, and won't start, won't even crank.

I've had a look, no obvious engine damage, there's oil in the engine, but a smell of fuel on the engine oil cap. When it's cranked, the engine turns over slightly, but then seems to be locked.

I'm thinking a rod, or maybe a valve has gone and got stuck. Does it have a timing belt/chain, maybe that's it (and if so, is it an interference engine, I've had the timing belt go on a d15b2 civic before and had to replace valves)
Am I on the right track?
How hard will something like this be to fix (note, I've no engine hoist)

I've not taken it apart yet, I've just got back home to try and sort out a trailer to get it here to work on.

Cam timing is via chain and all metal sprockets. They can stretch and skip, but that should not prevent cranking.

It's not unheard of to have the cam snap off.

They don't break?

She says it was a clunk and the engine died... I've just hiked the 2 miles to it and took a look. The engine won't turn, starter works, moves slightly, but nothing else, so something seems jammed.

One quick way to find out is to remove the left (front) rocker cover and observe the valve action while you manually turn the engine forward and backward - If you can. If none of them are moving, it could be a chain, If some of them are moving, it's likely a snapped camshaft.

3.1s have a reputation for running great right until they die catastrophically. As BB said, camshaft breaks, oil pump drive seizure, etc...