Headers for my 71 Demon 340.

They will fit. At most, a ding here or there. There's no major surgery, And you only have those two choices, for the best chance of zero troubles.
And the TTIs are thick,heavy, beasts that last decades,and hold their torque on the heads,( none of these 1-year wonders.). My TTIs are circa 1999, and still going, altho, since I bought them uncoated and ran them also for 5-winters on my DD, the merges collected salt and where they did, they rotted; my fault. No biggie to repair.