I say get the proper “box weave” welting from Thirdgen and paint it body color. I just did it on my ‘46 Merc and had no issues at all. I carefully did all the trimming and cutting darts and bolt holes into the welting for minimal installation hassles, and I “pre-bent” the welting where the turns were the sharpest before I painted them, and shot them with the same single stage enamel I used on the body. I’ve had zero cracking issues. And I think unpainted black welting would look bad on any color other than a black car. Zoom in to see how the welting looks on my car in Modern Blue. It’s a key part of a restoration, and I think doing it right will be worth it. Just my opinion.