I also have one of those Lee molds. The bullet shoots on par with the LBT one that I shoot. Although I don't get as high of a percentage of keepers out of the Lee. That old saying "ya get what ya pay for."

My sad story is that I had a LBT mold on order when Veral went under.
As far as gas checks go even though they dropped the pressure from 50,000 psi to 48,000, you still don't need them. Veral Smith told me that the 475 and 500's don't need a gas check. Even at full house max loads. And it is just now getting common to find Gas Checked molds for the 475.
I have been running full house loads in my 475 for 4 years. After a break in with jacketed bullets and fire lapping I get very little leading.
As far as meplate the closest that I can measure is about .335 I can't see it being over .340. It sure isn't .360 I wish it was. Maybe the newer molds are that dimension but I hadn't heard of any changes in it.
Will