I had to buy a tail pipe expander to enlarge a couple of the female pipes.
The hose clamp can pull the pipes together. The wedges can be used to move (spread ) them apart.
Can use insert the side pipe into the headers before you install them on the car? Work on them till you can get them close to slipping together. Some are made with one pipe just a little bit longer so you can start it first. Second pipe a little short then the third with the fourth the shortest.
Then install header onto car. The side pipes should be close. Now use the hose clamp and wedges.
Good luck. I think slip fit pipes are a test in life
