Few Questions Its been awhile...... topic

Hey all, Its been a while since I've played with any new roms and finally got a chance to come and check things out to see whats out there.

WOW there's been a lot going on and I started reading thread after thread and searching to find out more.
Right now I'm on HyperDrive RLS16 with TWRP
and looking at a few roms and most say you have to have MJB 4.3 bootloader/modem and you CAN NOT downgrade back.
I searched for more on 4.3 bootloader to find out more but couldn't get a clear answer to this.

I've came up with some questions that I couldn't find answers to....

1. Whats the difference between MJ2 and MJB?

2. I've tried to download the bootloader from here but file not found http://forum.xda-developers.com/show...9&postcount=23

Is this the same package http://forum.xda-developers.com/show....php?t=2252932
http://www.androidfilehost.com/?fid=23269279319197285

3. How to confirm what bootloader I have? Ive looked in TWRP and DL mode and couldn't find.

I think I flashed the MJ2 bootloader my mistake will there be any problems in going to MJB?

Thanks in advance for any information you guys and the DEVs are great keep up the good work..