If you do not mind I might make some suggestions.
1st off a standard stock v8 v12 transmission will hold a lot of power. Somewhere around 500-550 whp/tq.
Do not get rid of the belleville spring washers. They promote even distribution of the piston pressure to the clutch pack.
I will kind of go over all this quickly. B1 really is not a huge problem to begin with because it only holds power in 5th gear. Simply there is no torque left. If you want to upgrade it you can get a different piston all together. It has shorter teeth on it. Unless it you get one with 3 clutch packs in it and are planning on making 1000hp do not get to upset about it.
The key points to focus on in the transmission are the k3, k2, and b2.
K1 again if it is really low on clutch count and you are going to make a lot of power.
If you need to modify for more clutches there are literally dozens of different assemblies. Normally the v8 transmission have more than enough.
B2 is the hardest to do anything with. Unless you are making north of around 700w/tq do not worry about it.
K2 there are quite a few different pistons. It is pretty easy to get the clutch count up to 6 total with the right combination of steels. If you want more than that you can machine the piston.
k3 you want to get the v12tt k3 clutch housing. It holds 6 frictions or 12 singe sided.
I use single sided clutches on all my builds now except the ones that are not available and have absolutely no issues.
And lastly again I mean this. The stock transmissions are pretty good. I ran around 3-350whp through a bone stock used transmission that was a glycol replacement from a c230k for quite a few years with the standalone.
I run 400+hp/tq through a stock v8 transmission now and probably will never have to replace it.
I will say that tightening up the clearances was a good thing to do when using the standalone.