Ok, here it is. I received my coil last night from Hilkoil. Kudos on the superfast shipping. I ordered it Wednesday, it was on my porch the next afternoon. I chose the 18TL kit due to it already having nice, swept bends to get to and from the HWH. Also, I measured and this appears to be the largest, factory built model they offer that will fit into the side of the 1557M w/o much issue. I drilled the holes to 1 1/2" versus 1/18" so I could use my super oversized and tapered face boiler disconnects on th coil. They allow the coil to be placed just off of the side of the firebox, partially in the flame, but not to interfere with the fuel area. The tapered nose fits into the 1 1/2" hole and seals it from the inside, as well as the gaskets and washers supplied from Hilkoil. I used the remaining section of the disconnects to bush out the threads on the coil outpust so a fiber washer and the other pain of supplied jam nuts could be used to seal the air jacket back up again. I will be moving the HWH next to it tonight and plubing in a simple thermosiphon setup w/ a boiler style temp/pressure guage. Hopefully, Sunday morning showers will be using homegrown hot water. LP is $4.90/gal here and I can't take it anymore. They came and filled me up this week, it was almost $500 bucks. I called them and told them to come get their tank an LP ASAP and credit me the difference.
As soon as i figure out how to post pics, I will.