Hi tubed1,
The Chinese CV-181s measure 4" from top to bottom, not counting pins, plus almost 2" diameter at the bulge, vs. 2-1/2" for a typical straight-sided 6SN7. Pin-outs are identical (as they are with mil-spec US and European VT-231s and Russian 6H8Cs. There will be very minor variations in Mu, heater current, etc., amongst different brands, vintages and runs, but all are interchangeable.
If you're handy with a soldering iron and have a solder pump and small vice, and are on a budget, restoring the Soviet-era 6H8C metal-based MELZ tubes can give you a sound right up there with the best of the Chinese tubes. I emphasise *metal* based because the later Bakelite based 6H8Cs aren't up to hi-fi snuff except as for splitters or maybe buffers: I wouldn't use a Bakelite one in a pre-amp or driver board for voltage amplification as they're noisy. Drawback to the metal-based MELZ tubes is the crappy solder they used to affix the pins to the wires coming out of the bottle. Heat up each pin, suck the old junk solder out, and flow in some good stuff. The base-to-glass glue was, fortunately, crappy, too. So if you want to go out you can de-solder all 8 pins, remove the base, and re-tin the leads coming from the bottle with some good stuff. It's time-consuming but after some practice you can do two tubes an hour's time.