The standard BOINC credit calculation is done using the benchmark. Each computer multiplies their benchmark with the time it took to do the work unit, and submits a claim to the server. If the benchmarks are accurate, the claims should be the same, or at least similar. The server does some averaging and sanity checking, and grants an equal amount of credit for each valid result.

For some projects, it is possible to work out how much credit should be awarded either ahead of time or by analysing the result sent back. This doesn't work on all projects, and usually requires a lot of extra code to be written.

I think you can use BOINC View beyond your private network, but it would require careful setting up of firewalls and stuff. Using an account manager, though, you should be able to detach and reattach a host if it stalled. I've never tried it, though.