my machine is very similar to the one in the catalog, but I believe it's older. The other machine I've seen with that square/round needle plate had a fiddle base, but had the more typical Eldredge/national type tension release. The only other machine I've found with this tension release is the Jennie June, but it looks quite different.
Will be fun when I have time for more research, but for now I'll still be looking for a machine that takes the longer shuttle.
I kind of wonder if National sold a converson kit - it would just be a slightly shorter shuttle carrier.