Bountiful is, IIRC, a hybrid of butternut and Japanese walnut/heartnut.
They should be capable of pollenizing one another - provided that pollen-shed/nutlet receptivity patterns are compatible - which, you've determined is not the case.
I don't know patterns for either of these cultivars... pecans, we usually have pretty well-defined pollenation times form most well-known cultivars...not so much so for 'minor' nut species, like butternut/heartnut/hickory, etc.
Sounds like you need another butternut, heartnut, or buartnut (or more than one) that will pollenize these two.

Looks like Ernie Grimo & Charles Rhora are the NNGA 'experts' on these species - they may be able to make recommendations

Here is a link that might be useful: NNGA experts

I thought I would share what I found out . The Westfield heartnut started shedding pollen on April 30 . I saved pollen and some of the pistils emerged on May 7 . Most of the pollen was gone on the tree but a few late catkins were nearing the end of pollen shed . I hand pollinated a few on May 7 probably not ready and pollinated most on May 10 . It appears I have a good set of nuts .

Now for the Bountiful butternut . Pollen shed started about May 17 and still going . Took awhile to find any female flowers . This tree seems to have good pollen shed during female receptive time . So lack of nuts on this one seems due to few female flowers . This should correct itself in time . Picture shows spent catkin and one starting to shed pollen .

Here is the female flower .

My BB is alone except for local black walnuts and doesn't have a problem. It's been extremely loaded some years. It's about 24 years old.

I thought I would update this . This year the Westfield heart nut set a fair crop . The Bountiful butternut continues to slowly increase its set of nuts . So it seems both are self pollinating . The heart nut sheds pollen before the pistil is ready to receive pollen . However as the tree gets larger there are enough late catkins shedding pollen to set a fair crop .

Thanks for updating. How do they taste?

Taste is good .

I'm not so sure how alone my BB is. Found out they're very willing to sprout. The trees are also not completely immune to the disease that is killing butternuts off. My tree is probably going to be gone in 10 years.