Just a couple of words of caution here...
To make a 25W60 like this, the oil's going to have to contain an appreciable amount of Group I Bright Stock. For those that don't know, this is stuff that you get from the Propane De-Asphalthing of Vacuum Residue (the heaviest and blackest stuff you get from an oil refinery). It will be very high in sulphur, nitrogen and aromatics. There are no Group II, II+ or III equivalents of Bright Stock.
Now don't get me wrong. I personally like Bright Stock. A couple of percent in a PCMO can work wonders, especially for things like diesel piston cleanliness. However, because of their high benzylic hydrogen content, they can be extremely oxidatively unstable. A very high ZDDP treat and a splash of Moly will only go so far in mitigating the problem and the TBN is worryingly low. Just don't try extended oil drains on an oil like this. In fact check the dip stick frequently because when this oil breaks, it will likely break very quickly. Leave an oil like this in too long unchecked and you could easily see its KV100 top 4000 cst at which point, your problem becomes one of 'how do I drain this stuff from my engine?'.
Of course, as a blend component, this stuff is the mutt's nuts (which is how you might benefit most from it).