Getzen 300 / 351 / 345 / 350 ?

[blap73]

I've been looking at the Getzen student trombones and I see that the 351 is pretty well liked for an entry horn. Looking at ads I see a lot of "300 series", the occasional '350', '345', etc. I've seen the Getzen serial number page (which doesn't help me on this question)... From photos how can you tell the difference between the various 300 series horns? It looks like earlier than the 350 has a knurled bell nut (instead of hex), and maybe earlier ones have a conventional spit valve. I also see some difference the the slide crook end bumpers. I'm sure some of the listings are saying '351' out of ignorance, and likewise some '300' ads might actually be a 351.

My old 1960's Reynolds saw a lot of abuse and is in pretty tough condition. Hadn't picked it up and tried to do anything with it since the 70's.

[Conn100HGuy]

I had a 451 (351 with rose brass bell) that I really liked. It's one of those "student" horns that does very well in a jazz/big band setting.