Glen, You say you have the correct plates. To help you a little bit I need to know what the stamped letters on the plates are.
For example, you are looking for B150....but like most plastic plates they come in 16 cell and 24 cell, and in each configuration they are the same color, gold for that size.
I have a feeling your planter has the sprocket settings set for 24 cell plates, so if you have 16 cell plates in the planter the plates are turning too slow...resulting in longer spacing between kernel drops (and lower population).
Count the "openings" (cells) along the outside edge and let me know how many there are...16 or 24.
Some plates would have B150-16 and the companion plates would have B150-24. And same color.
Historically, when the 290 planters were built they came with the sprockets set for 16 cell plates because plant populations were very low in those days. As populations got higher and higher the operator just changed the sprockets to make the plates spin faster. At some point those plates spun too fast which made very uneven stands or too many skips.
Then plates started appearing with 24 cells; then the operator set the sprockets for 24 cells and the plate rpms slowed down. At todays pops often running 32,000 and higher even 24 cell plates are really spinning fast and the operator needs to slow the tractor for accurate seed drop.
One big favor you need to do for yourself: Go to a JD dealer and see if he can get you an operator's manual for a 290 or 490(4 row). Or go to EBay or somesuch source or maybe someone on the JD forum might have one to sell to you. That manual tells you exactly what you need to do for proper sprocket settings.
I wrote a long article a few years ago about these problems as they come up in the springtime. I was in the seed business big-time years ago and grew up with plate planters and the transition to plateless planters.
I am going to try to find that article and see if someone can help me figure out how to forward it for usage this year.
Glen, please get back here with what you are finding on your plates.
LA in WI