First, to answer your question........Leupold makes 2 piece bases. You can also use any (as far as I know) one or two piece base(s) for a remmington long action.
I use Badger Ordnance picatinny rails on my Wby actions. (They are listed as made for remmington long action.) Then you can use any Weaver style rings. Badger, Night Force, Burris Signature are good ones.
The single piece rail is expensive, but I believe it is much more solid than two piece mounts. It also gives you much greater flexability with your scope placement and allows you mount other items, such as angle indicators or levels to the rail.