Pre-Alembic modified I do believe, Edwin. At least, in Grateful Dead Gear (really good source - and I'm so cool I know a guy who got name-checked in the "Acknowledgements" section.......*), pg. 35, Bobby says he got the 345 in '66 because Bear & Tim Scully wanted to mess with the guts, and the back door was their work.
Peter
*For those who have not read this seminal work - or at least not read the Acknowledgements - said name-check is to one Edwin Hurwitz.