Oh, the answer was always there: the Mangusta Parts manual that Bosswrench scanned and posted on the POCA website shows the fiat 1300/1800 part numbers for both the short and long hangers, both are still available;
4066081 long front
4035175 shorter rear
Still, this doesn't mean a perfect fit--at least, it seems the Ansa DT0127 and DT0137 Mangusta mufflers have a shorter front strap, either/and the Hall headers I have position a little lower (even though I bought this combination from Hall in 1985). Good news, adjusting the strap is easy enough.
You may have seen that "Ansa Classic" will make you original headers or mufflers, each for about 2000 euros each...I can't find it now, but CarID had Ansa mufflers for about $750 a pair, apparently USA made with polished stainless (instead of chrome) tips.
For the life of me, I cannot find gaskets on the shelf that fit...I'm still using ones I cut by hand--Lee