I grind brass & bronze, sometimes aluminum or non-magntice stainless from time to time.
With one or 2 parts, i use the traditional hold-down combs, one on each side. Most combs are about 1/8" thick or less, so you should clear if they are sucked down almost flat. (Needs some angle to grip). I also have sections of chopped up handsaw blades to use similarly, for thinner material; usually only on one side, holding the part to a rail or parallel.
Holding 4 parts at once is more than a little risky.
Like assuming you could hold them all snug for milling lined up in a vice for one go, without paper.
It is possible to mill snug pockets in a magnetic parallel or even just soft steel block. Or between 2 blocks that you squeeze together while activating the magnet. Dirt, burrs or non-parallel surface can shoot the .001 tolerance in a pocket, though.
Lastly, toolmakers vise & parallels. Again, only a couple at a time. Though if your vise is wide and accurate enough, 4 across could be held with paper against the moving jaw. Trust your gut - if it seems iffy, it probably is.
Part in pix is aprox 18" long, 1/4" thick.
smt
PS: you really did not give much to go by AFA dimensions.
Thin long parts or very wide parts may be tricky both to hold and due to heat distortion.
I always grind stuff like this (except when held in a vise) on auto with slight infeed (.005"-ish) per reversal, & coolant.