I have a .375x2.5 made from a shot out .303 by the late Mr Neil Speed. I acquired it together with a couple of other Lee Speeds from his estate auction. It shoots to the original sights point of aim and is a delight to shoot and very accurate. Whilst it is not an original .375 I am very pleased to be its caretaker, given its history.
You won't be disappointed with with your .375, once you get it going.
The LS original 10 shot .303 magazine that Mr Speed modified can, on occasion, load and feed nicely but I have to position the cartridges perfectly. As my intention was to take it hunting on occasion, this is not very satisfactory so, 18 months ago I ordered and received a single stack magazine from Darryl in South Australia, he is a member on this forum , he also made me a beautiful fish belly mag for another rifle. whilst the single stack loads and feed 4 rounds perfectly, it does not look like a genuine .375 magazine, so I was pleasantly surprised to learn that Darryl has recently modified a no 1 mk 3 mag to look like the real thing,double stack 6 rounds and he has figured out how to modify the tabs so that it feeds properly. so I have ordered one of these from him.
I plan to spend some time on my computer getting to understand things like loading photo's to this forum. once I do, I will post some photo's of all the lee Speeds.