I had one built with a Jungle Carbine enfield, it was ok, a bit of feeding issues that were eventually resolved, and a bit of a rough bore. I had issues with the Smith taking more then he said he would, and he kept the old .303 barrel and said it was part of the cost.
Mag was modified to single stack and held 5 rounds or something, but I think they could be made to feed with staggered feed as well.
I built a zebra wood stock for it, shot it at the range a few times and then it just ended up sitting in the safe so I sold it.
I picked up a marlin 45-70 barrel for like $100 a few years ago and would like to do something like the enfield mountain rifle thread and make an adapter essentially but I'm not sure I'll ever get around to it.
For a build like this you pretty much need a new barrel, and there is work needed to get it to feed properly, I was probably into it for $1K+ and probably sold it for a couple hundred less then I paid, not including my own time scabbing together a stock, but it was fun and unique, just not really any better than a lever at the end of the day.