After seeing a few water well circuits landed at discos in a pit or shed, it occurred to me (duh), that the 'in sight of' rule applies here. A customer has one (fuse box) that's had it, and likely pre-dates the 200a service panel. Questions are; is 'in sight' required and must it be fused or is a pullout ok?

It does not need to be fused. A motor rated snap switch would work if it was rated for the HP of the pump. (not uncommon with small house pumps)
The "in site" thing usually has a bit of wiggle room in it. Just look at the intent. You don't want someone coming up and flipping the switch while you are working on it. I have also heard this referred to "as far as you can accurately throw your Kliens". You don't need to see the switch itself but you need to be able to see someone screwing with it.
A lockout capable disconnect will also work, wherever it is, although that is not my favorite method since LoTo is a foreign concept to too many people in the service business.

NEC Article 100 Definition of "within sight, in sight from", or "within sight" is to be visible and not more than 50'ft distant from the other. If the equipment requires a disconnect and one is not visible ("within sight"), and more than 50ft away, it violates NEC requirements.

I assume we are talking about a submersible well pump?

That would need a disconnect per 430.102(B).

However check out the exception, specifically (b).

It basically says the disconnect does not have to be in sight if it can't be in sight.

Check out the definition of the word "impracticable" as compared to "impractical" as used in 430.102(B) Exception (a). You might be surprised.

I am not surprised, I was counting on it.

It is imposable for the disconnect to be in sight from an underground motor.

I think for the purposes of this discussion we are talking about within sight of the J box where the well tech will be disconnecting the wires going down the pipe.
Our plumbing can be above ground here so you usually have the RNC coming out of the ground on a post, that will carflex over to the box on the well head. If you have a motor rated switch on the post and the final connection is made in the box at the well head the rule is fulfilled. The other way this is done is to have the disconnect in the box on the side of the house where the RNC goes down. That is where mine is (actually in a pump shelter for the "house pump", bladder tanks and control equipment.)