What type of motor do I need for a ranger 230v bass boat?

It’s a bit underpowered by conventional thinking, but the real test is whether it does what you need. 

If you find that it struggles to propel your boat against normal local tides and currents, then it will definitely lack the power to weight safety margin needed if one day you’re facing a predictable periodic stronger tide/current. It will also potentially be insufficient if you’re running against a normal tide/current and the wind is also against you. The hull may struggle to achieve acceptable progress if you carry passengers or any cargo as all of that bogs the hull deeper into the water.

But if it does what you require and there are no concerns about the above scenarios, then keep it. The advantages are that it will use less fuel, and parts should be cheaper.

As someone else suggested, the minimum output for that hull mass would typically be about 50hp, but there really isn’t much difference in maximum hull speed on a hull of that mass between a 40hp and a 50hp motor. If you choose to upgrade then if it’s another two-stroke motor then aim for at least 70hp, and if it’s a four-stroke it will definitely need to be more.

A $100 40hp Johnson must have been really old though, so you also need to also consider that old worn outboards tend to have lost a lot of their performance unless fully overhauled. You can also make a significant difference if your hull is kept clean: I’m always stunned by how many I see which are caked with aquatic flora and fauna on the underside because the hull is never lifted out of the water and periodically cleaned of all growths which add a lot of parasitic drag.

Edit: Just done some research on your boat model as I’d never encountered a 230v before.  

They were rare animals even when new. Be very careful not to add anything even close to maximum suggested power output: sadly many boats of that age have a reputation for severe rotting internally below the shiny fibreglass exterior. Back then a lot more internal structural members were made of timber, especially so with the transom and the structural wooden stringers within the hull floor. Some models were designed with longer term repairs in mind, the 230v was not. 

So if the transom  or stringers have gone rotten they have to be cut out and the cutting back has to continue until you find solid timber again. The reason so few of the few 230vs made have survived is that owners often found that once they discovered rotten timbers it was too late to save the hull. 

So putting a powerful or heavy load onto the transom risks the hull breaking apart at speed. Unless you know for certain that the internal wooden structure is rock solid. Checking it needs a few strategic holes to be drilled to examine the wood.

They were likely referring to the length of the motor, a shallow draft Bass boat will need a short shaft motor, and of course they are rarer than long shaft motors

You're underpowered as others have said, should be substantially more for performance.  However, if the 40 does what you want it to, carry on as you are.

The guideline is 1 hp per every 25 lbs of boat weight, so a minimum 50 hp motor to go  20 mph over smooth water.  

Your 40 horse is underpowered, so expect sllower speeds and a decrease in fuel economy.  

My guess is a 75-90 hp was the most popular choice for that boat.  

Boat will need a motor from 30 to 50 hp.  You have the right motor.