Steve,
The previous owner is in Florida with his new Evolution (some guys have a really good life :-) ), but thinks they have the part number back in Ohio and will let me know when they get back. So, that may work.
I just thought I could save the time of trying to match it up by having the part number.
I think you could easily, and very accurately, compare a paper/cellulose filter to your K&N.
First, carefully observe manifold pressure and rpm obtained with the K&N, then see what the results are with a good quality paper filter (same runway, temperature, barometric pressure, etc., of course). If the mp & rpm are no lower, the K&N is giving you no more performance.
Hopefully you are already doing oil analysis (OA) on your engine and will have pretty good baseline numbers established.
So, next, compare the silicon (dirt) and wear metals (aluminum, chromium, iron, copper, etc.) over the next couple of oil changes. I'll bet you will start to see a decline in both dirt and metal with the first oil change (using a paper air filter) and will continue to see a decline over the next couple of changes until things stabilize at a lower level.
Doing the above will take all the conjecture, opinion, etc., out of the filter question. I can really only deal with hard data.
In case you're not already doing OA, here's a link to a sample aircraft OA. Put your computer pointer over any of the elements and it will give an explanation of them and from which parts the metal could be coming. Actually, the pointer over any of the blue highlighted areas will bring up explanations.
Hope this is helpful to anybody not familiar with oil analysis.
Blackstone does not charge for the sample kits and only charges when an analysis is done--$25 each or, as I do, pay for 6 at a time and it's only $20 each.
I would also highly recommend using their vacuum pump to pull the sample through the dipstick tube. Allows one to pull samples without draining the oil. Makes it very neat, clean and quick. I will sometimes pull a sample in the middle or last third of an oil change interval just to monitor what is happening with the engine. The vacuum pump makes this a clean 5 minute job. I use it even (before) when I am draining the oil.
Bill