This seems like an essential and rare book for the 1938 LaSalle owner to have..... (not mine, just happened to see it).
https://www.ebay.com/itm/123044611517
Eldorado James
Dated late 1938 but from the very few pictures it seems to cover the 39 model year. They don't say if it also includes the V16 either. I have a true 38 databook which does cover the V16.
Steve is correct. Published in late 38 for the 39 model year.
Bob