I agree that those Duncan SD-1's sound wonderfull, and the neck pickup in particular is as warm and punchy as an HB-1 (can say the same for some Dimarzios as well). I don't know what strings u have on the SF-4, but with 11's tuned standard, it should have a semi-hollow acoustic type resonance that a 71 solid M-75 would not typically have.
I will say when I write "HB-1" I am generally speaking of the early ones 1970-1971, and your post is spot on tone-wise. 90s Guild pikcups seem hotter like 70/71 (whether they be Guild, Duncan, or Dimarzio). The Fender buckers actually sound great as well (just got a questionable review online that went viral, thats all!)