Again, I'm not running one of these valves, nor do I know anything about them... However, they have an online chat feature on the Inlinetube website, and I initaited a chat with someone at the company, and they confirmed the disc/disc" proportioning valve is a 50/50 split front to rear...

The valve is also made in the USA, if that matters to you. So this may be an alternative to buying a valve and modifying it... But again, I don't have or run one... Just throwing this out there as an option someone might like to consider...

Does your PR101 Proportion Valve have a proportioning section?
Jul 12 1:38 PM

Yes it provides a small amount of proportioning.
Michael C · Jul 12 1:41 PM · Appreciate

What does it proportion? (Meaning that the common definition of a proportioning valve is that it sends less pressure to the rear brakes than to the front brakes.)
Jul 12 1:42 PM

Yes, there is a slight bias between the front and the rear.
Michael C · 6:20 AM ·