I'm reading the guide and have myself confused.

Rate Spread is not applicable to loans that are NOT subject to Reg Z.

I'm "thinking" HELOC's are not subject to Reg Z but I can't seem to find that in any of the new 2018 updated information. Is this still the case?

For open-end lines of credit, a financial institution complies with §1003.4(a)(12)(i) by relying on the annual percentage rate for the covered loan, as calculated and disclosed pursuant to Regulation Z, 12 CFR 1026.6.

HELOC's can certainly be for consumer purposes and, if so, are subject to Reg Z. Lots of banks do this. Maybe your institution doesn't make open-end loans or HELOCs to consumers.

If you do offer HELOC's to consumers, follow Randy's post.
If you don't offer HELOC's to consumers, all of your open-end credit would be reported as NA for Rate Spread.