I have just installed the latest WP-o-Matic. It seems much improved, and I congratulate you on your ongoing development!
A couple of years ago, MyShadowSelf provided code to truncate an imported post:
He was using wpematico, which is coded differently, and this occurred some long time before the current updating of WP-o-Matic began.
Is there any way to tweak the current version of WP-o-Matic to bring in only the first X words of content? I assume this is something you'd add to your future "advanced templating", but darn it, I want it now . . .