Manual disc brakes vs power disc brakes questions

Unfortunately, I've never seen a new "parts store" 2-bolt 1 1/32" bore (Aspen/Volare) master cylinder that wasn't cast iron.
BTW i just got 2 new volare aspen 1-1/32" MCs from rock auto. They were supposedly remanned, however all the parts including the reservoirs are new castings. These were closeout for $12.27 each so i bought 2 of em. One has an aluminum body, one has a cast iron body. Both of the ones i recieved have a groove in the back of the piston for a manual brake pushrod o ring retainer. Plus the threaded holes for the brake lines on these are not metric, but are standard SAE thread.

I still need to buy the 4 bolt to 2 bolt adaptor firewall adaptor. The doctor diff one looks to be the best quality made one. The mopar perf one looks like its just hacked out of a 1/4" plate of aluminum.