For a cheap, effective, and reliable (can't believe those 3x words could be in the same sentence) go for OEM R34 GT-t calipers, with 310mm discs. They still use the same DB1170 brake pads.
All you need to do is enlarge the bolt hole to accommodate the 14mm bolt off the R34 caliper, then the discs, calipers, bolt straight on. Just need to grind off the lip on the disc shield behind. Some remove it altogether, however it's recommended it remains there to avoid debris being thrown at your rotors.