I found the answer to my question by going to the source - it finally occurred to me that I should email right to Alaska Railroad. (Sometimes I'm dense and slow...) I also asked about a seat assignment we are wanting. Here is what I was told in case anyone else would like to know:
Thank you for your email!
In regards to your inquiry, our ticketing staff will assign seats a couple of days before departure. I have entered a note in your booking regarding your seat request. We are not able to confirm seating requests, however, we will do our best to meet any request.
In regards to carry-on luggage, each passenger is allowed a carry-on as well as a personal item such as a purse or backpack. Please remember each passenger can also check four pieces of luggage free of charge.
Please do not hesitate to let us know if you have any further questions. We look forward to seeing you onboard the Alaska Railroad in February!
I had read in one place only two checked bags and in another place that the Winter Train allows four checked bags per passenger. This clears that up too. We should only have one checked bag each but it's good to know one can have more.