I forgot to update this thread, I forgot I even started it, my memory is so shit these days I can't even recall why I open new tabs 99% of the time,
but I digress.
What I came up with is moulding the header or pipe into a cardboard box with a mixture of 50% pure cement powder and 50% ready to use mortar mix. Both can be had for about 10 bucks a bag from the hardware store.
The pipe is marked in direction and upright position for the pressing. The pipe is then painted in any old aerosol paint to help it from corrosion attach of the highly caustic environment that is wet concrete/motar, and also a means of non sticking the cement when it sets, so a sort of mould release, it also allows the mould to break around naturally as the lot is pressed by many tons of pressure. Note that a clear top coat spray can works best as you can go over the entire section and not lose the marks drawn earlier, otherwise you need to avoid the marks using opaque paint.
Mixing the mixture should be done as dry as possible while still uniformly wet, so like a uniform dough consistency. This allows the setting to be even stronger than a more normal level of wetness. The strength was the key. I went through many iterations of resins and filler, then tried mortar but still fell short of it crumbling before I got any meaningful pressing. The strength of the mould prevents pipe distortions and bending out of line. It allows all complex shapes.
After the pipe is placed in a carefully cut out box, you aim to pre-level the pipe to have the exact spot you want to press in a hydraulic press to be flat from the first go, this is important as you can't pack or shim the block of mortar afterward as the bottom needs to fully supported and flat.
Once that is level, you pack in the mixture to just under where you want to squash and indent your pipe, give it a little jiggle to make sure all the air comes out. Leave it to set for 3 days to a week. Week works best I found. I also found a clamp and blocks of wood to help hold the box walls together from slumping due to the wetness of the cardboard. Another tip is for multi pipes like in my example where the motar will go in between, I sealed off those gaps with the sellys wall plaster ready to use filler, it's very light and fluffy and will comes out easily after everything is done and will save trying to get rock hard morar out and damaging the metal in the process. You could use blutac or something else that can do the job. I had that and it worked well.
You need to get some tissue paper or cloth and block the end of the pip some distance past the mould. Then slowly add packing or construction sand and using a yellow tounge, a rod or wooden dowel depending if you have bends to go around or just straight, pack the sand as hard as you can, slightly damp sand works better. If dry sand is uses, you can pre-pack it before moulding which makes it all easier to handle, but damp sand will cause pitting and rust left that long. So damp sand is worth the trouble of packing the already set in mortar pipe as much as a pain it is. Once it is packed back past the mould a distance the other way, plug that end with tissue or a cloth to stop any sand loosening up and falling out.
On your press, you need a big eff off slab of steel as the base to support the block of motar and pipe.
Then you get your pressing tool, a long enough solid square bar or block of steel, or even a round solid slug with the base of it as the pressing surface, line it up with your marks and slowly pump the press down. Adjust if needed, then when you feel it's right, press it down to the level of desire and normally around that 5mm of so the pressure builds up quickly and the mould starts to break down the guts of the pipe lengths, the sides towards the surface break aways and it's ready. You will find the following results.
My recommendations is a soft mild to low carbon steel. Pacemaker in my case are already that nice soft steel that is easy to form and bend without springiness. Most pipe by the meter from an exhaust shop and even SS pipes are springy as shit and struggle with good form and the moulds just struggle to keep from breaking before a decent indentation is formed due to how much pressure is needed. It's not impossible though and many of my practice pieces were from that springy steel, it's just harder work with bit less clean results, but none the less they are as OEM looking as can be anyway. Once using the soft steel, the results are awesome!
IMG_8210.jpg
IMG_8211.jpg
IMG_8212.jpg
IMG_8213.jpg
IMG_8254.jpg
You do not have the required permissions to view the files attached to this post.
I just used some heat and a planishing hammer when I clearance the headers on the 300zx ls1. And a sledgehammer for the trans tunnel 
