Bud, Read your post looking for support, well, I switched from shooting 3 under for the past several years to split finger at the end of the summer. I felt really comfortable/confident in my shooting all year, but I tried to focus my practice sessions before the season on stump shooting with one arrow. I tried to make it as realistic as possible, canting, shooting while kneeling, sitting whatever. Bottom line, for me, while my 3 under vertical style worked well at 3-D shoots and backyard targets, it was just more practical at typical stickbow ranges to shoot split due to better arrow control, more focus on the target and less on the arrow. My whip longbow was also noticeably quieter and "felt" better on the shot. I'm a hunter, not a competitive range shooter, and I feel for me this style fits better.
As far as the process, I changed my anchor from index finger in corner of mouth and feather on nose (3 under), to middle finger just behind my canine and base of thumb tucked behind the base of my ear. This kept my elevation change to a minimum. Lowered my nock point down about 1/4 inch for good arrow flight. Didn't take too long to get confident out to 25 yards which is about 5 further than I like to shoot anyway.
I'm certainly no expert, but hopefully this helps a bit. Good luck!