There are a ton of options with single shot bolt actions. If you want a falling block design, then the Ruger #1 is probably the top platform for custom builds.
For all out accuracy I would chose a solid floor bolt action Like the 40x single shot.(No
opening in the bottom for a magazine).
There are other actions made this way and some custom actions also.
These actions are very strong/rigid and bed very good.
I love the single shot falling block rifles and have 5 of them but the two piece stock and the
design of the action just can,t compete with a bolt for accuracy.