Frank, your layout speaks to me! I am a Pennsylvania railroad fan. I LOVE the layout plan. I take it each block represents a square foot? If that is the case, you curves are sweeping and could accommodate long trains with no problem.
You can have a lot of fun with this layout, especially depending on the era you wanted to model If you are looking at PRR, then you have GG1s that would be perfect in Altoona. Marklin offers these and they are true to scale. Heck, you have enough space that you represent a slice of the Juanita shops! Also available for PRR in this era is GP7s (AZL with radio antennas), GP9s (MTL), heavy-weight passenger coaches (just released this past year from AZL), and coming up later this year Light Mikados (AZL). PRR GP35s have also been released
If you want to go later, with the NS era, you have SD70Ms that were released by AZL, SD70Ms with flared radiators will be released in the next few months (AZL), SD40-2s (MTL), and GP38-2s (AZL).
Of course there is a good selection of rolling stock for all eras! Take a look at the AZL website for some idea of the options available:
http://www.americanzline.com/Sixty you say? You have time!
Rob