There are 3 different movements available in BP 1661x. The ETA clones and DG2813s have non gen-spec crystals with straight side edges and the cyclops is in the ETA/DG native dial window position (1mm right of Rolex window).
So of course you would want the 3135 movement. It has a gen-spec crystal that can be replaced and it will take a gen dial. The movement is an SA3135, which is the worst but even ARF's SH should be replaced with a VR IMO.
None of the BP versions will take a gen bezel or insert without some expert modding. They all use the 8 sided wire clip to attach the bezel, the insert is only 37.5 wide, gen is ~37.65mm. The outside of the rehaut is a smaller diameter than the inside diameter of a gen crystal retaining ring, so a mod to fit a gen-spec bezel needs a filler in that gap. Laser weld or epoxy can work. I converted one using epoxy almost 4 years ago, it has held up perfectly.
The inside rehaut engraving can be sanded off but there's actually a fair bit of material that needs to be removed to erase the engravings completely. This will usually result in floating minute tics (space to the rehaut) where there should not be any.
Note the difference in space between a sanded and a stock BP rehaut on two 16570s. Black dial has sanded rehaut. You can also easily see the difference in rehaut thicknesses at the ledge.
Also one of biggest complaints about the BP 1661x is the wide lug chamfers. They can be narrowed with some careful side sanding of the case.
BPs are often passed over due to these issues but I like them for what they are and have probably 5 of them. The smaller insert worked well in one I converted to a 14060, hah.
But since you want to do an accurate rep, you would be better off looking elsewhere for a base.
Here is a BP (on top) next to a TC with drilled lugs
Also check out this thread
Https://forum.replica-watch.info/for...other-st-build