So.....I see in your profile you’ve already got an ‘08 E350. What engine? And why not use that to create the camper best suited to your needs? Plenty of upfitters out there these days putting out really nice stuff, certainly updated from a 17 year old SMB build, but it would be more $$ in the end.
Both seem well priced, although not having seen them....who knows, but a 7.3 with very low miles is certainly desirable, if the layout works for you.
You could always gut and rebuild
.....I only say that cause that’s what I just ended doing to our 7.3 SMB RB50 after owning it for 13 years.