With my Loki 1000w PSU, the standoffs included in the kit and labelled as PSU standoff in the manual do not fit - or at least would require so much force that it feels they will damage the threads. The correct standoffs should be 6-32 Female-Male (i.e. both threads are 6-32) and are tricky to get in UK/EU but I've sourced some from a supplier and these fit absolutely fine. I'm wary of advertising anything here, but I have loads now and can arrange supply to anyone who needs some, just drop me a message.
Not sure if this is just me, as I've received message from someone who thought they fitted fine, but on a different PSU
If you want to mount the SFX-L PSU to the SSD drive area this is possible, but you need these standoffs for the PSU so that you can clear the power plug when you refit the front panel. I've done this for my SFX-L PSU to allow use of the Founders Edition exhaust slot at the same time (which requires removal if you use the PSU bracket and an SFX-L power supply).