Here you can see the Double Eagle Model 15’s fine tuners as a separate piece from the base plate and required bolts from the bottom.
The sustain block is made of brass and is slanted near the end, a characteristic that it’s possibly of Gotoh/Double Eagle origin. That being said, this Model 15 style has also been seen with a cheaper die-cast sustain block.
This FRT-4 copy seems to have been somewhat poorly made, but people sometimes mistake these for an actual ’83 FRT-4 or FRT-4 prototype, which it definitely is not.