Emboldened by progress so far, without any significant whoopsies or rework, I proceeded to the 2 main supports.
Having recently bought a paper copy of Textbook of Advanced Machine Work, I had seen how planning out work was a relatively straight forward but necessary step. The book is replete with Sequence of Operations charts, mostly starting with “oil the machine” I planned out the sequence of operations so that I didn’t machine myself into a “can’t get there from here” scenario.
To that end I sized and squared up the 2 main support pieces. I marked out the 3 shaft holes and drilled then using a N drill, followed by an 8mm reamer. This allows me to use some 8mm ground HSS tool steel as alignment pins.
Using the 30mm boring head I cut the decorative scallops. Using the table stops made setup simpler for the second of each scallop. Basically move the table until work pieces touches the boring bar, set that stop. Then set the infeed stop to the correct distance. Without a DRO this works for me.
Similar setup was done for the large cutout. A slot drill allowed me to plunge in and then run to the 2 stops. Two smiley pieces of aluminum are now ready for some boring stuff.