Can't get Pro Parts headers to fit.

I spent some time looking for my old install posts, nada, here goes.
I haven't put in fenderwell in a long time but to shift the engine around, take the weight of the engine off the mounts with a floor jack, with board to protect the pan, start by loosening all the bolts/nuts holding the mount brackets to the engine and loosen the bolt thru the k-frame, then use a bar, fl jack handle, whatever's nec to shift motor towards where you need it, wedge it there till you tighten everything you loosened. There are 318 van/truck rubber insulators that are approc 1/4 in thicker if you need height. As mentioned, shims can be made and used.
Sometimes loosening/shifting/raising the trans mount can help.
Get the motor close, then I would do driver side, I think, lol.
A lot depends on how " bent " your car is since factory.
It can be very challenging to avoid having to ding a tube, but I haven't put in fenderwells since . . .
Good luck.