Probably the last omission from the Centaur family in BDB. Centaur Jr. was a single engine, 96 inch (so 1.5m) upper stage proposed for Atlas:
https://web.archive.org/web/20220406014718/http://www.spacelaunchreport.com/atlas-eff-centaur.jpg
It would have likely had a shroud of similar diameter. Coincidentally, this is similar to the H-1 upper stage:
https://web.archive.org/web/20220406014752/http://www.spacelaunchreport.com/N1-N2-H1.jpg
The H-1 used a Delta 8 foot shroud and a 98 inch diameter stage, which also works out to 1.5m (I'm not opposed to it being slightly fatter). They're both common bulkhead stages, it's possible that Centaur Jr. would have had Centaur-style insulation panels, but I haven't found much info on that, so a H-1 style stage would probably cover both of them (for the actual H-1, LE-5 and the UM-129A kick stage would also be needed, but I don't know if that's desirable for BDB).
The existing hydrolox stage for Delta is clearly based on Delta K proposal, being considerably longer than either of those, and with a tapered avionics section meant to terminate in an Agena shroud. It would not be a bad idea to add the new variant (if not going with jettisonable insulation) as a mesh switch for that tank. Engine mount could be shared without issue.
Probably the last omission from the Centaur family in BDB. Centaur Jr. was a single engine, 96 inch (so 1.5m) upper stage proposed for Atlas: https://web.archive.org/web/20220406014718/http://www.spacelaunchreport.com/atlas-eff-centaur.jpg It would have likely had a shroud of similar diameter. Coincidentally, this is similar to the H-1 upper stage: https://web.archive.org/web/20220406014752/http://www.spacelaunchreport.com/N1-N2-H1.jpg The H-1 used a Delta 8 foot shroud and a 98 inch diameter stage, which also works out to 1.5m (I'm not opposed to it being slightly fatter). They're both common bulkhead stages, it's possible that Centaur Jr. would have had Centaur-style insulation panels, but I haven't found much info on that, so a H-1 style stage would probably cover both of them (for the actual H-1, LE-5 and the UM-129A kick stage would also be needed, but I don't know if that's desirable for BDB).
The existing hydrolox stage for Delta is clearly based on Delta K proposal, being considerably longer than either of those, and with a tapered avionics section meant to terminate in an Agena shroud. It would not be a bad idea to add the new variant (if not going with jettisonable insulation) as a mesh switch for that tank. Engine mount could be shared without issue.