The search facility is littered with posts from PRR on this very issue.
In short, there is no direct replacement for the 6386.
Not only are remote-cutoff triodes relatively obscure in the grand scheme of things, but dual remote-cutoff triodes are the proverbial rocking horse's manure.
The 5670 is not a remote cutoff tube, and as such will start to distort, due to the plate becoming current starved, above about 12dB of GR.
To my knowledge, the best option - if you don't want open-wallet surgery for 6386s (or risk buying fakes - seen them!) - is an adaptation of the 6BA6 Pentode. Manley match a pair of 6BA6s in their T-Bar mod, and the Transfer Curve is virtually identical to the 6386.
If you search under 6386 at Prosoundweb, you'll see some transfer curves posted by Lab member Larry, illustrating a comparison between 6BA6 and 6386 - pretty close.
I won't name drop, but I was told a few years back about the 6BA6 conversion by a designer who'd been through the same rigmarole. If I'd known what I know now, I would've just trusted his judgement, but hindsight has proven his judgement to be correct.
IIRC, PRR suggested giving the 6ES8 a try - anyone?
The PCC189 is used in Jakob's variable-mu compressor, as well as the EAR 660. I love the EAR - very smooth.
Justin