Ok, so I ordered the kit(s) Monday, it shipped Tuesday and arrived today. That was fast, but then I am just a couple counties away from MP in northern California.
The instructions are detailed with pictures. I got the basic version of the kit(s) with RK-47 capsules. The basic kit includes 4 WIMA caps (2x .68 and 2x .01), 1 diode (no spec mentioned) and one 0 ohm resistor (jumper can be used instead), backplate lead wire, mount and screws.
The most difficult part was disassembly; pulling parts off and keeping holes clear of solder after part removal (even with a solder sucker). I only felt like I had a couple questions along the way but they were answered by looking at pics on their installation guide page (how to attach the backplate lead to the capsule for example).
Getting the capsule on the mount was a bit of a trick too getting the screw holes properly aligned. Basically it is best to start a thread of one screw then the second before completely tightening. I probably spent about 2 1/2-3 hours total from start to finish on the first mic.
The booklet has the user start with disassembling the mic body in detail, then part removal and replacement (C3 and C4
get replaced by the .68 caps with the .01's paralelled at their connections under the PCB, the diode replaces D3, R1
is replaced by the 0 ohm resistor or a jumper wire and the cap on the underside of the PCB is removed, then finally swapping the 2 & 3 pin connections for the XLR), then capsule replacement (though the booklet shows the RK12 capsule which is one reason I had some minor issues in my head only) and even the headbasket and caulk mods. Plus a suggestion to paint the body.
Not really concerned with the caulk in the body yet but I had removed the mesh layers in prep for this a while ago.
So I plugged her in (as suggested before removing extra component leads to be sure things work) and sure enough it worked! I grabbed an unmodded 990 for comparison. I recorded just a couple takes of VO to test and read some dialogue through both 990's and an AKG C 3000 (original, not the B) that I have at home (I have a couple U 87ai's at my "office" which I intend to compare as well). Compared to the stock 990 there is more of everything. The stock mic sounded hollow and fuzzy compared to the mod. The mod sounds more natural and up front. You need to get right up on it for any real plosives or sibilance. Not so for the AKG which is chock full of pops. There is more pronounced low end on the AKG which almost sounds hyped when compared to the modded 990. The RK47 seems to have a good upfront midrange with natural sounding top and bottom. The mod definitely made the mic better, but not certain that it can out class a Neumann. Definitely useable though.
I have another 990 (3 total) and 4 SP-1s that will get this treatment.
The advanced kit has more parts and allegedly can extend the low end a little more so I may go that route in the future. I got my 990's years ago for around $60 per and I got the SP's for $40 per so I am still around $200 per mic including the upgrades when all will be said and done. I can't complain about making mics I wasn't using viable and useable. Not to mention doing the work was fun.
I wish the kit were a little more instructive as to what the components swapped/removed affect in the circuitry but aside from that if you can work a soldering iron and have a basic understanding of electronics the kit is fairly ideal and easy enough.
I'll do the other one tomorrow after work.