Long story short my dad owns 1 of the infamous 225 four stroke Yamaha outboards that were built between 2002 and 2005 that have the hot exhaust corrosion issue..

I bought all of the exhaust and oil pan parts for it that go in the midsection but after pulling the powerhead the flange of the exhaust on the powerhead where it meets the flange on the midsection is eaten up for about 2 inches.

A new powerhead short block is 5000 k . this one has some hours on it but runs like a Swiiss watch

It is possible but it will be almost impossible to find someone to do it that knows what they are doing. It will probably need machined after it is welded too.

It's very doable, but as Warparty said, finding qualified individuals is tough. One thing to remember is that as welders, we don't have the liberty of knowing the alloy or cast composition. That being said, some castings are FAR cleaner and nicer than others, thus easier to machine and weld. Being an engine block, from a large OEM, I'm going to assume it should weld very clean without issue. The only precautions you need to take are that any gaskets/plastics/etc near the weldment are going to need to be removed, and the block in this area at least, will have to be insanely clean and free from oils, dirt, etc. I do very little repair work, but when someone must have it done 9 times out of 10 I have them bring me part that is hot tanked because most welders don't want to deal with a filthy, oil dripping part. I tell people often that TIG welding aluminum is akin to a flawless paint job... the welding part is easy, it's the prep that dictates the results. Also, being a flange mating surface, it would be a good idea to at least have the entire gasket area faced off to ensure true.

There are specialized places out there. Many aluminum heads/blocks and other things get repaired all the time, even from catastrophic events.

I don't have any personal suggestions for you.

A place like this: http://midwestcylinderhead.com/services.php#marine
That you can get references on will hopefully be able to get you going.

Thanks for the input guys.

The whole bottom of the motor is one big flange of the same level so I could almost reface the exhaust portion of it with some self stick sandpaper mounted on a aluminul straight edge like a level..

Getting it rolled over on it's side so the welder has access will be interesting as it is still fully dressed and i hate to have to tear it down,

Getting it clean will be a bear also. I have read that heating it to 700-900 degrees over and over will help to clean out the metal.

Can anyone recommend a good welder with in a 130 miles of Naples Florida that has the experience to do the job?

take it apart, have a machine shop cold tank it to clean all the crap off it, then take it to a good welding shop. NOTE: if the welding will change a critical dimension on the part, take it to a machine shop to measure out the part before you have it welded, so they will know how to re machine it after the welding is completed

stripping the block is not an option.All it is is where the exhaust exits and mates with the midsection. the area is 3 by 4 and maybe a 1/4 inch thick and is surrounded by a waterjacket.

This is the repair i am doing but the pics do not show the problem i am having with the bottom of the block.

http://www.thehulltruth.com/boating-...on-repair.html

Brian Orlandi of Orlandi Performance who is a paid commercial member here welded the water inlet on my cast Imco shorty several times for me before I got it just right for water pressure and to stop cavitation burn.