There is a guy over at RFC working on a billet receiver for the Marlin 60, however, its nowhere near being ready for the public...
not to mention being prohibitavely expensive at the moment...
The hairy bear about switching barrels in a Marlin receiver is the Pin-in barrel...it requires a Press.
Both to get the OEM barrel out, and to put the old barrel into the new receiver.
And...if you screw up, you can easily ruin the barrel or receiver, or both.
RFC has a couple nifty threads about what can go wrong...and what can go right doing a swap.
I'm not just Trigger Happy, I'm Trigger Ecstatic!!