Can you just dump the pfsense cfg and just parse and collect the objects? you can run the "viconfig" or just grab the "config.xml" and find what you want.
Then convert it to a lingo that is FortiOS formatted. For only 100 rules and 1k objects your can police and cleanup the rule sets at that time if required
I've done this a hundred of times with grabbing the config.xml and taking out interface and system host objects for importation manually. YMMV but if you have a good script-tool guy, you could craft a script.