I’m making a 100mm hardtail with a steep-ish head angle and it looks like the top of the fork stanchion will be very close/graze the underside of the downtube with the bars rotated. Rather than go for a bent tube, I was considering putting a small dimple in the 38mm 853 DZB DT (butting 1.1-0.9/0.6/0.9), about ~70mm down from the HT junction on the underside. This would be in the 0.9mm zone and only need to increase clearance by ~5mm for comfort.
I don’t think that’s a great idea. It’s probably the one area on the one tube that’ I’d leave alone as much as possible. If you can’t get the clearance you needed by moving the DT up the HT then one thing I’ve done a couple of times is to braze a bottle boss in the area and bolt in a rubber/plastic stop.
The head tube is pretty short so trying to keep the DT at the bottom. I haven’t got the fork yet but think it may clear by a few mm with changing the lockout knob to a lower profile. Worst case, I fit it up after brazing the frame and braze in a bump stop as you suggested if needed. Would also help protect the TT from handlebar dings.