I suppose there will be a gazillion answers to this but:
No, the Straight-8 (or rather a PDP-8 without a model letter) is very
different from a PDP-8/a (with model letter "a"):
Pictures:
Straigh-8:
http://www.sciencemuseum.org.uk/images/object_images/535x535/10296909.jpg
PDP-8/a:
http://pdp8.co.uk/wp-content/gallery/my-pdp-8a/00001.jpg
Cheers,
Pontus.