<snip> ...but the problem is that none of them are backwardsly compatible with the standard 72-byte save area. </snip>
Totally untrue. The documented 144-byte (and 216-byte) save areas can be passed just fine to a routine that uses a 72-byte save area. That is why they were designed the way they were. The one thing that you lose is the ability to "chain forward" when reading info in a dump. That has never been reliable. <snip> but it is because with the 64-bit save area formats for amode 31 programs you are saving your low-halves in the caller-provided save area as normal, but you save the high-halves in *your* save area.] </snip> The "because" is not a valid conclusion. And in only some linkage conventions do you save the high-halves in your save area. <snip> Is there really no possible way that it could be accomplished? </snip> Read the manual. Peter Relson z/OS Core Technology Design
