Spitfire Headers

I haven't seen a set of these though I've read about them. It looks like they are designed for a weld on collector? Or can a slip on type be used?
Yes they will need a weld-on collector, I have a set of 4 of these
2 1/2" Universal Mild Steel Flange Exhaust Pipe 2 Slotted Bolt Hole OVAL sf-008 | eBay brand new that I will add for free,if your interested!

coupler flange.jpg