Every keg has a 2" tri-clover welded onto it. Just flip the keg upside down.
My two cents I'll try to help if I can BUT. If I was wanting a keg with a bottom drain here is what I would do. Just as the quote says turn it upside down.
This my opinion
1. cut the bottom from the keg
2. cut the top rim off the bottom of the keg
3. remove the rest of the remaining bottom from the side
At this point you have a keg with easy access and nice straight sides. One thing upside down no handles but a pair can easily be make and tig welded to side.
Second.
4. A false bottom in my opinion is a must.
5. If bottom space under the neck is a priority I would go with a 2 inch cap and go to a 1 inch size fitting. like 90 degrees elbow, and short length of pipe to another cap 1 1/2 for the reduced size of piping.
To settle the fears on size of keg necks here is picture where I took two necks one upside down and use them to hook up my keg on the rig.
Here is how I like to do kegs as mention above for nice straight sided keg no sharp edges to get by and it can be done on the bottom of a keg
Here is another option this brewer wanted to put his heating element straight up from the bottom. Tig welded a 1 inch half coupler in the bottom
That is my two cents not saying its the best way just the way I would do it.
If a larger false bottom is needed I do have some material left over from a large project. I would sell very reasonable to get rid of it. its 1/16 thick 3/32 hole on a 5/32 stagger.
God Bless
Dominus Vobiscum
Swagman