Basic grip stuff
1) Because this 2H BH is primarily an "assisted" left FH, you want to decide your grip for your left/top hand first.
2) Both hands need to hold the racquet with the thumbs (i.e. no crease) almost parallel with the forearms. This connects the kinetic chain of the body to your left arm.
3) As a result, when selecting the grip for your bottom hand, you want to find a bottom hand grip so that both thumbs can be comfortably parallel with their respected forearms. I think the readings suggest pairing Eastern FH grip with a "between Eastern and continental BH grip", or a SW FH grip with an Eastern BH grip. But, in any case, the thumbs will tell you what works for you.
Left hand dominance
1) To set up very strong left hand dominance, try this during shadow swinging. Have both hands gripping the racquet with just the 2nd, 4th, and 5th fingers. This throws dominance heavily to the "hand powered by kinetic chain", which here is the left hand. Your right arm will kinda "disappear" in the stroke. Once you get this committed into muscle memory, then when actually hitting balls, you can mantain the 2-4-5 (or a 2-5) with your right hand while using all fingers for your left hand. When you feel your left hand is comfortably dominant, then you can use full grip for both hands.
Eastern FH
1) Safin's unique among the left hand dominants, in that he uses a "classical" Eastern FH. Meaning, he actually traces a shallow smile pattern (or "U") with his left elbow. So, initially, you want to practice with just the left arm.
2) You take back the racquet by letting the left elbow swing upwards and counterclockwise to about nipple level. Like a pendulum. At the same time, you try to preserve the angle of the elbow bend. It looks like you trace the left half of a shallow U or "reverse J" with your elbow.
3) When you want to initiate the forward swing, you just let the elbow drop or slide back down, launching your arm forward. So the motion is actually like a shallow pendulum, but it looks like a mostly straight swing.
4) When you're ready to attach the other hand, the right hand is completely passive here. It isn't part of the pendulum/smile pattern; it's just there. Therefore, you would concentrate on taking the racquet back with merely the left arm and letting that initiate.
5) Probably should noted: His "Eastern FH" is really special. Yes, most players have a pendulum motion, but they use both hands to pull the racquet back. Their racquets swing much more around the body than Safin, whose forward swing moves almost in a straight line toward the ball. Agassi has a similar effect, but he of course does it with a 1H BH/right hand dominant setup. This also helps to explain why his forearms rotate less than others through the forward stroke.
Back/left shoulder above front shoulder
1) Atunit turn, make sure the front/right shoulder is slightly dipped. Looking down at the ball helps with that.
2) Just make sure the back/left shoulder is above the front/right shoulder through the takeback and whole stroke.
3) If you got the left handed dominance down, then this is pretty easy to do. If you don't, then it's hard. So, working out the left dominant dance and Eastern FH swing first helps.