I have a 1969 Falconet in 12 gauge. I recently stumbled across a longer (28”) barrel Than my current 26” set on eBay and bought it at a great price. I liked the idea of having a second barrel set at a tighter choke pattern

I dropped the barrel onto my receiver and while I can get the barrel to close on the receiver, it’s tight and somewhat difficult to re-open. Additionally, The forend won’t latch.

I’m hesitant to mess with the receiver and foreend as I have a perfectly wonderful over under now. What I assume I need is some gunsmith work on the new barrels to get them to fit better on the receiver and forend.

Any thoughts or recommendations?

You need someone familiar with fitting that gun. Those people are pretty rare. If you can find the fight guy, it sounds like you can make it work because everything on your new barrel is tight, that means material has to come off your new barrel. I would start with Franchi service and see if they have someone there that has the know how and whatever tools may be needed. If you can't find someone at Franchi then someone that has worked on guns with similar action might take it on. Someone who has done Browning type actions could probably do it.

I notice this is an old post, so I will PM the poster, since he probably is not monitoring this now.