Any history or background on series IIA brake reservoirs?
I'm in the throes of replacing the master cylinder on my 66 FFR IIA,
and was thinking of replacing the fluid reservoir. It's fairly beat up
from too many wrenches over the years.

I'm trying to do a "trust, but verify" about replacing it.
I looked at the parts diagram in a Haynes restoration manual, page 212,
and it shows a reservoir like I have - with two outlets out of the bottom of the can.
Page 84 of the 1966 FFR manual shows a different perspective drawing, but the same
2 outlets on the bottom can.
They look exactly like the Girling reservoir I have on my '59 Healey 3000.
The Girling repros (and replacement parts) are relatively inexpensive - see here

However -
The green bible, and our sponsor, only show a (pricier) reservoir with a bottom and a side outlet, and no other options.
When did the side outlet first appear? Other than being stainless, is there any difference in performance
or operation?