The v7 and v8 are practically identical. So everything would be reusable in a v8. The lens should work in a v5 to v8... Not entirely sure on this though. Some other parts such as the fan, controller ports, ... are reusable on all v4 to v10 ps2s. Power supply "should" work in a v4 to v8, never tried mixing and matching these though.
What did you do to the motherboard? Did you attempt to mod it? If not, and it just suddenly died, it could just be as simple as replacing a fuse.
Just make sure the MB has the same plug in connectors as your old MB as some MB might be in a differant area for these hookups and your version might not have the right lenght of wire made to reach a point on a MB that is not similar to yours,but if similar i can`t see why it shouldn`t work just that some MB are the r-type for r-type lasers but the eeprom can be flashed to work with your laser if need be.
The v6 or v8 MB should be similar as long as it has the same mounting holes to fit into your ps2 it could work,i haven`t done this myself so i`m not totally sure on this,but i can`t see why not.Good luck!