I was going toss my ideas out there until I reread your opening post and realized they don't fit.
I'll mention them so everyone can chuckle at my lack of reading comprehension.
Marlin 336 in .35 Remington, oops bottleneck cartridge
450 Bushmaster, oops again AR platform

anyway...the 45-70 in a Marlin big bore is very alluring.
If I buy another rifle that what I want.

enjoy,,,i would keep the 99