Engine Paint and Raw Water Pump

I am trying to get my engine ready to drop into the boat. (I have to get the boat ready too!) The engine when I bought it had a missing heat exchanger. The heat exchanger has rusted through due to having seawater(raw water) sit in it for a long time. You can see in the picture below that the block had a little bit of rusting and staining from the heat exchanger.

I think that a clean engine is helpful as you can see when leaks start etc. So I need to clean the rust and paint it. I sanded off any of the chunky rust which there was very little. Mostly it was paint that had lifted from the rust below it. I taped off the exhaust ports then I painted on a rust converter and let it sit overnight.

Last night I went out and warmed up the garage. It was in the low 40's here! Brrrr. Then pulled out the Yanmar gray paint. Or not! Yanmar wants $16 for a single can of spray paint! $16 bucks I don't think so! Home Depot sells Yanmar gray as gray Rustoleum for $4 a can. Yea I went with Rustoleum, call me cheap. But hey they use this paint on oil rigs so it has to be good right?  I had a few pieces off the engine that needed paint too so I went crazy and sprayed them too. (By going crazy and painting parts you can imagine how "wild" my life is! OK back to the boring stuff.) Here is a picture of the new shiny parts.

Oh look there is the alternator spacer I said I had to paint. (Fourth item up.)(Look at the extremely boring post before this one!)

The raw water pump. people complain about the raw water pump being hard to get to on this engine. I can see why. The starter is only a few inches from it so it is difficult to access it and get the impeller out. I'll work out some way to make it easier to get to so if I have to do it in a seaway I will be able to without to many bad words spewing from me. Oh and  I think I will get some extra screws for the cover as they are small and I know I WILL drop them into the bilge never to see them again.
Anyway I pull the cover off the raw water pump and see the impeller looks to be in OK shape. There are only a few nicks in it but all the vanes are there. My impeller just pulls out with no "C" clip or retention device to make the job harder.

But my real question here is the pump housing. It appears that the impeller sat for a while. There is a bit of evenly spaced "lumps" in it. I'm not sure it is corrosion as much as it is just dried seawater. You know how it leaves a hard residue or better yet a scale? The amount is really small as far as now pronounced it is, but should I try and remove it? See the green lines? That is what I am talking about.

So let me know what you guys think. I know there has to be a few good marine mechanics out there!