So... I'm skeptical as to it being correct, but some sources claim that the lowest-end 233mhz PowerBook G3, the cacheless model, came with a PPC 740 instead of a PPC 750 on the CPU card. If someone has one of those in their junk drawer and is willing to yank the heat sink off it to see if it actually *is* a 740 rather than a 750, well... that would be a source for a BGA 740. Not that that would really help you with a Duo 2300c if it uses a QFP chip. It *might* be usable on a 1400's CPU card if you could bribe someone who has access to BGA rework equipment to help you swap it out, as it seems at least some 1400 CPUs are BGA. (Pictures of the Sonnet Crescendo 1400 cards show a BGA CPU...)

To be honest I'm finding it difficult to find evidence that QFP PPC 740s existed at all.