Bit odd though that anyone would trade of 3 gravid females, that have been bred to morphs, for a bunch of ASF's. I'm always a bit leary of any deal that seems to good to be true. Check this breeder out on Fauna BOI or ask around here. Insist on taking your ASF's to him so you can check out the conditions these females were kept in. I'd hate to see you do a trade for what you think are nice captive, gravid females and end up with 3 hard to care for gravid imports. If he did indeed breed these females, he should have exact records for you to review as well as the male snakes on site.
I'm not saying to not do the deal, just be cautious about it.