[MrMagoo]

OK, now I am playing "wannabee genius inventor". I have spent hours fabricating a device that spreads the two pieces apart. Version 1.0 yielded a spread of approx 1/8 inch before bending out of shape. Version 2.0, reinforced, is currently in development. I love this phase of an operation where you make the call to invest mucho time and effort on something that may prove impossible, and perhaps even cause irreparable damage and/or bodily injury.

Update: It is actually working. Got 3/4" before ran out of spreader bolt length.

Notes: This is only doable because of the brackets that are welded to each tube on both header and side pipe pieces, against which the spreader is pushing. Were it not for that I guess I'd have to weld something on in their place. You need to do both sides at once. Liberal doses of PB blaster doesn't hurt and probably helps. Every once and a while I just get out the rubber mallet and start whacking. Not sure if that does anything. Strong bolts required. I'm using 1/2 grade 8 which is probably overkill, 3/8 would do. To prevent bending version 2.0 uses angle iron to push against the brackets.

Update 2: It worked, I got the header off. One of the brackets snapped off near the end. I'm lucky that this only happened to one of the four brackets and I was able to continue.