According to Hodgdons website 50gr of IMR 4198 is a max load for a levergun so they're likely ok to shoot in your rifle, However,
we're always cautioned to Work Up To a max load when changing Anything, including, primer, powder, bullets, you've changed the Rifle. I'd work up to a top load for That Rifle.
Also, the Speer 350 is a longer bullet from the crimp groove to the tip of the bullet so I doubt the cartridges will feed in a levergun, if you loaded them in full length brass. They'll be a bit long but as you said were fine in your #1.
I've used Speer 350 in a Marlin 45-70 but I had to load them in Hornady's 45-70 brass, they're shorter but that's a different situation.
This is precisely what I do. I use the shorter Hornady brass from their FTX cartridges to allow these bullets to run through my 1895 Guide Gun. As mentioned, these bullets were designed for 458 WM velocities and as such tend to penetrate deeply. I load them as a combo Elk hunting/Grizzer bear defense load for dark timber hunting.
Frog---OUT!
