There are 2 belly plugs, one just ahead of the front belly brace and the other is just behind the rear belly brace. The are difficult to see in all the photos I've seen so far and I don't have a good shot myself.

Since the front tubesheet is welded in there is no flange joint between the tubesheet and the barrel to collect scale and this hugely simplifies washouts. We plan to make a N&W style nozzle that can be threaded into the belly plug and then rotated to be able to wash the front sheet seam and then chase the mud down to the mud leg. Those items combine to create the ability to eliminate the front plugs. As a veteran of many boiler washes of the 1385 I can testify as to what huge pain those 2 plugs are in trying to both remove and replace them without having to open up the front end, open up the netting and then crawl around the blast pipe to retrieve them when dropped.

mld

TrainDetainer,
As our Aussie friends might say "Fair Dinkum". The combustion air inlets were placed with a goodly amount of input from Gary Bensman and we are taking his judgement and experience in this field seriously. As to the front end, we plan to use the same arrangement that we took out. It steamed well in its career here and didn't pull holes that we could tell. It is one of the places where it seems it ain't broke so we don't plan to fix it.
mld

Overmod a question if you don't mind. Earlier you asked about " fine points of 'tuning' the Master Mechanic front end baffle and lip to optimize the rebuilt flow". Could you please elaborate on exactly what you meant? I have read and helped with a few restorations that did have blast nozzle modifications but know of very little else being done over and above original work. In the early 1970s as a young guy I spent a lot of time in #1385s smoke box trying to duplicate the spark arrestor box/netting that had rotted out. Felt like I lived in there for a while. So I am some what familiar with the "petticoat" adjustment and modifications to blast nozzles {not that I grasp all the voodoo but know about them}. So are you talking about the plates in front of the flue sheet on smoke box end being adjusted higher or lower? This in relation to the "optimize the rebuilt flow". I do not question anybody's ideas or questions other than to learn more about how boilers work and what can be done to make them work better.

Also can somebody shed some engineering light about the importance of radius in the knuckle areas of formed firebox parts and the relationship pro or con of having the seam close to the radius. Not looking for rocket science but general idea of how stress works in relation to those knuckles and if the seam riveted or welded to close has any known effects? For example the AK #557 picture to me looks like it was done the way I thought it was supposed to be done v/s the seam being much closer or squared off like some stationary boilers are made. Again I offer this picture of #557 {off the progress report from their month update}http://www.557.alaskarails.org/restore/progress-reports/2019_09/Firebox-on-display.jpg. Again this is not to question others work known to exist but to expand my understanding and hopefully others who want to understand more. The probability of me helping replace rear tube sheets in the near future are slim, but you never know? I do end up in some of the strangest of places. Regards, John.