Heat Riser Removal??? ... 68-70 340 HP Manifold

Looking for info on removing the heat riser from my right-side 340 HP manifold.

The more I play with it the more I feel like I'm going to break something and the flapper is going to be a permanent resident in the down tube...

There is plenty of advice on buying a replacement heat riser, but I can't find any "how-to-remove" info anywhere.

Any advice is appreciated.

Thanks!