Hey I got a 4 into 1 for my 750k. I believe it's a Kerker. It has the flanges to put the screws through, attached to the pipe. Are these pieces welded on? Are they supposed to move? because the the flanges are too close together to make it through the frame? 
I don't know if I'm supposed to pull the pipes a part or what. I'm sure its a simple explanation.
I'll assume this is going on the 1974 CB750k listed in your signature?
Does the engine still have the spigots in the exhaust ports? If so you'll need to remove them and install studs for those flanges to fit over, then secure the flanges with nuts. Be sure to replace the copper gaskets, they're in there, it may not look like they are..but they are. Probably so covered in black that they blend in with the exhaust ports. They come out with a little encouragement, but be careful not to scratch the port.
Slide the 3 of the flanges down the pipe a little until they stop, then with the remaining flange at the top of the head pipe, place it up to the exhaust port and set the flange on the studs, secure with two nuts but don't tighten them down..just hang the pipe for now.
Then slide another flange up and repeat the process, then another and another. Then tighten them all finger tight, then them all a little more, it doesn't take monster torque to hold them on there, if you're using new exhaust gaskets they'll crush pretty easily and seal well.
Before and while tightening, you may want to give the back end of the header a firm rattle with your hand to make sure everything is lining up well and nothing is binding.
The rear mount for a Kerker pipe is a long hanger rod that attaches to a threaded stand-off fitted in place of the right rear shock's top mount, if you don't have one, you can easily fabricate something to fit, just don't let the muffler rub on the brake pedal mount. Some have made rear mounts that attach to the passenger peg mount and swear by them, but the geometry isn't quite right... it just doesn't seem right to me although it does show off the shock more.
Cheers, I hope it helps.
-A
