These pages don't really cover the 345/375 to 380 upgrade, since I don't have good info on it (or EEPROM image files). If someone were to send me details, I'd be happy to add them. Presumably a procedure similar to the one described here could be used to upgrade a 345 or 375 to a 380. You can follow a rough guide, but I won't make any promises.
First some terminology:
|345||50 MHz 68030||thin rackmount|
|375||50 MHz 68030||rackmount|
|400s||50 MHz 68030||s|
|400t||50 MHz 68030||t|
|380||25 MHz 68040||rackmount|
|425s||25 MHz 68040||s|
|425t||25 MHz 68040||t|
|425e||25 MHz 68040||e|
|433s||33 MHz 68040||s|
|433t||33 MHz 68040||t|
|433e||33 MHz 68040||e|
The s workstations have a weird tower-smashed-into-a-minitower case style, also known as a strider case. Here are instructions for upgrading a 400s to a 425s or 433s.
The t workstations have a normal, thin, tower case style, also known as a trailways case. Here are instructions for upgrading your 400t to a 425t or 433t.
The e workstations have a thin desktop case style. There are no instructions for upgrading an e machine, since they all shipped with 68040 processors (though you could still get a faster oscillator and 68040 for a nice simple speed boost).
The 345 has the same case as the 340, but its guts are the same as the 375, namely same RAM cards and same upgrade path. I'm under the impression HP never shipped a 68040 version of this box, but there have been reports of people upgrading them. I don't have access to this hardware, so all I can do is offer a rough guide to upgrading your 345 to a 380.
The 375 is in a standard 300 series box with 4 or 8 DIO-II slots. The motherboard, like the 400 series has a 68030 daughterboard that can be replaced with a 68040. Uses the same RAM cards as the 345 and 380 (and possibly 400 series). The 380 is just the 25 MHz 68040 version of the 375. I don't think HP shipped a 33 MHz version of this, but I'm given to understand that it the 380 can be upgraded to run at 33 MHz. Again, since I don't have access to this hardware, all I can do is offer a rough guide to upgrading your 375 to a 380.