the 6in chop saws have a 5/8 arbor, 4 1/2 grinding wheels are a 7/8 arbor so that's a no go. I'll have to check out the grinder chop saw contraptions.
It surprises me that no one has something like this on the market, it seems like it would be popular.
Kidding me? I can pop out of the MTR, Wanchai, walk half a block, pick from among several, ready-made, only a few of them even Chinese.
But still.. just look in the packaging of many of the goods in blister paks.
There is often a thingie off in one corner as resembles an old skewl sparkplug washer.
A "bushing" however short it is, axial dimension, as "short" they need to be for the clamp-nut to be able to get a grip.
Those center blades and wheels with 7/8" holes - or "whatever", depending on size - onto 5/8" shafts. Or "whatever" depending on size.
Even if you have not previously had the need, if your Hell box is like mine, there are several already tossed into a corner of it and you may have simply forgotten what they were. They grow legs and are prone to have migrated into your automotive repair kit, or even plumbing or electrical. No need to make them. Just go in search, then pick the one that already fits.
As to the mini-chop saw? Have a look at the ones Milwaukee and DeWalt make for linear sawing of thin metal plate.
These resemble a scaled-down sawdust-making carpenter or framer's "Skilsaw". Some can handle dual blades.
RPM and tooling are already optimized for metal-cutting and in the small form-factor you seek.
All you need to DIY is a platen with fence, and a swing-arm. That should be easy, even if you have to cannibalize a brand-new and larger HF chopsaw, cheap as they are, or fab it out of oak and black iron, salvaged bearing, caster wheel, or PVC pipe for the pivot.
Those "cartridge" front wheel-spindles with bearings as accumulate when I update the motorcar are another source. Bearings may have gone noisy for a carrying their share of a 4 K lbs auto at highway speeds, but are still good for fifty years for a small saw, partial rotation only. They have lug ears on one end already, and wheel studs the other end as can be put to use to hold an arm.
2CW.. and too MANY saws, hand and power, to keep good account of, already!!!