I have mistakenly hot-rodded some 405 grain slugs in my Guide Gun. Still looking for some one to burn up the last 85 rounds for me. One experiences both recoil and torque when touching those off. If one is stepping up to 500+ grains slugs, I'd suggest one use modest loads. The 500+ grain rounds are popular in BPCR circles for use at longer ranges, but we're using rifles in the 10 to 15 lb range. Do let us know how things work out.
This target data has loads I fired in a #1 (where they are safe), but can't vouch for their safety in the Marlin. But they work in my #1 only in the Interbond version at cannelure length. The Interlock profile runs up against the leade in my rifle.
Perhaps lesser charges of 4895 would also work well in the 1895?
Sometimes, the air you 'let in'matters less than the air you 'let out'.