Hello I am rebuilding a 1989 Yamaha 115HP Outboard motor. When I was taking the motor apart I removed a bolt 1/2" in diameter 1/2" in length. When I removed the bolt the raised insert that the bolt threads into broke apart on one side (see pictures). It's considered a "plug" the hole is used for mounting a brass fitting with a nipple to run tubing from the motor to a pressure transmitter. This is only done when trying to diagnose a cooling issue. Outboard motors are water cooled, the foot of the motor has a small impeller the sucks water and pushes it through the engine block and then the water spits back out into whatever water the boat is in. In all my years working on boat motors I have never had to do this. To confess I should have never taken the plug out, I was just working away unbolting everything from the block. The rest of the block is great, the sleeves just need honed. So I am trying to save it. My plan of attack is take a solid aluminum rod, cutting it to 1/2" in length, and welding in place of the bolt. I still have the broken part of the raised nipple. So I plan on just putting it back into place and welding everything together. I have a Linde Heliarc 250 HF welder. I know I will have to prep the welding surfaces, preheat the block, and weld in small increments as to not over heat the block and cause further damage. What material should the solid rod be, 4036 or 5052 Aluminum? Pure Tungsten electrode? 4036 or 5052 filler material? Any advice is welcomed.