The JKF- JK Factory- makes a decent 1680- it is a cartel watch, but it can be a base to start from. It comes with a 2836 clone or a dg2813. With the 2836 clone, switching to a 2846 is easy but even the 2846s are hard to find these days. Case shaping is needed- esp. at the crown guards. But to do cgs, I have to pull the case tube which means I've trashed it out getting it out of there. Tap the hole, install a 7030 tube and a 703/704 crown. I use the WSO990 case tubes and have found a nice 704 rep crown on ali express for around $20. 702 assemblies are around- Athaya has them, but not sure how good they are. Drilling lugholes always helps. Bracelet is a 93150 rep, but it's decent. Haven't tried the fat 2mm spring bars, but the 1.8mm old style DJ bars work fine w/o having to enlarge the holes in the bracelet.
Crystal is glued on, but it's a decent top hat so I've left it alone. Bezel insert has a decent all acrylic pearl so I'm happy with it.
The JK comes in red or white, so take your pick. You could swap out the dial if you want- decent rep dials are around. DWOs, date wheel overlays, are also around- I just haven't found one lately.
JKs run from $145 to maybe $245, so the price is reasonable. I've been buying from Marvellous lately.
Next step up is a Viet case from someone like Ruby, but that will put you over $1K pretty quickly by the time you get a movement- not sure what will fit- a dial, and a bracelet. 93150s are tough to find these days, btw.