The retainer plates that hold down the helper springs? You NEED these to keep the compressed helper springs from shooting out of the channel at high speed.
I've modified and subsequently completely replaced the helper springs and retainer plates with a gas spring setup; I can snap a pic and measure the plates if I can find them in the garage. This is another area that you can improve dramatically over the SMB design. From memory they are 1/8" thick mild steel.
2008 E350 RB passenger 4WD SMB penthouse
2013 KTM 350 EXC
2008 KTM 250 XCF-W
2000 KTM 200 EXC
2003 Honda Element