RCA BA 86A

My first go to would be EmRR

Don't know about the factory timing mod.
It has been restored but not modded.
I want slower the attack and faster release

I should add an 86 with the official mod shouldn't act terribly different from a BA-6, on paper. If you like the BA-6 thing you probably don't want to change an 86. I don't have memory of people modding BA-6's for different timing, though I wouldn't argue against it so long as the 'famous' stock thing is still accessible. The factory dual timing mod is what became stock in the BA-6, and somewhat copied in all AGC's like Stalevel/Unilevel/etc, though those have comp type slow attack constants.

I have left my 86A stock with the exception to making a knob (inside, up front) to balance the 6sk7. Your not liking the attack and release of it may very well stem from the tubes being out of balance. This one drifts a lot and has to be balanced every time I use it so I know its working correctly. This one here is also a phenomenal sounding piece of gear. I rarely hit it hard as that's not what it was designed to do. I love it's warmth and color when it's doing it's thing with just a few DB's of compression.

Stock 86-A would be 1mS attack time and release described as 2 sec for 90% recovery after signal drops below threshold.  If you want much slower attack, it would require insertion of series resistance between the center tap of the side chain transformer and the junction of c-8/r-41. Don't be an asshole and drill weird non-reversable holes in old gear just to add 'features' that may not be appreciated in the future.

The design parameter is described with the intent that occasional gain reduction amounts of 3-4dB are normal operation, even though much greater reduction can occur.

The Limited Level control is in effect a threshold control which has some effect on ratio.

The dynamic balance and associated meter position is a balance check for the gain reduction tubes, the later version mod found in 86-B and C moves the hum control and adds an adjustable balance.

The dual time constant could be taken along the lines of the Stalevel or BA-6 schematic as example. You can get much greater sustained GR with the dual time constant, since the slower constant takes over on sustained peaks.

Hey that's great, man!  Good to hear it's being put to good use.  5 years isn't too bad for a great comp.

Very interesting.
So are you saying it’s not as straightforward as changing the value of R41
Or that changing that value has multiple effects by how it all interacts?

Ah, so you have version #1 then. 

You can change it some, but it's tied to bias and the meter zero blows up immediately.  You have to parallel something to ground, which means many times higher Meg value.  I detailed it in a GroupDIY post.  

There's an official RCA mod document for the dual timing like the BA-6, but no 86 schematic that shows it. You could put both timing methods in probably but likely have to drill some holes for a switch.  Boo.