My possible starting point, really like the bikes on this thread.
Just need to find the right tires in 27", any suggestions?
You could use the 27 x 1.25 Pasela, or...
the 27 x 1.25 Pasela. Honestly, I don't know of any other quality tires in 27". Paselas, especially the PT/TG ones with puncture protection, would be just fine for gravel.
You may be able to change that bike over to 700c tires, if you could lower the brake pads in their tracks by 4mm each (that's the difference between 27" (630 mm) and 700c (622 mm). With 700c wheels, you'd have a huge tire selection and more tire clearance.
But Paselas would get you going for now.