Grip, I do this, can I, should I, would you???

[Leftside]

I have been lurking and reading "Yoda" on other forums. Good luck on this venture.

I am a 52 year old, strong, not too flexable, 5' 9" 180 lb. male; golfing for just under 4 years.

Read too much, watched too much, and have converted a section of the garage into a clubmaker's shoppe

I have mutated into two strokes, a downward hit for the shorter clubs, and a wide long swing for the longer clubs.

To the point (sorry I ramble);
I have evolved into a double overlap grip.
Neutral, I guess an average amount of angle across the palm of the lead hand. Both thumbs on top of the shaft. The double overlap is the last two fingers of the trail hand (Lefty's like to use the terms lead and trail, as the conversion from "right and left" to "left and right" uses too many calories) nestled on top of the index and middle fingers of the lead hand.
I just read Yoda's post on the lead thumb being on the aft side of the shaft, and it obviously made sense to me, and also prompted this post. I adopted the double overlap during a range session many months ago. Nothing was working and I was in "WEEM" (wild eyed experimentation mode). The double overlap gave me what I thought was an instantly better release of the club. the shots were longer and higher. I have been using it ever since. All well and good when you just want to break 100, or more elementary in the beginning just want to move the ball forward into the air. However I am now wondering if I built myself a box from which low to mid-eighties, 220 yard drives and the 145 yard six iron are the norm?
I am thinking given the strength, the lack of flex, the 28 year martial art background, the 6 motrin a day I eat (and I still can't get the lead arm higher than my chest), that Hitting would be a logical goal.

So I want to Hit.

I am going to be working on stretching the lead out out with the trail hand's pressure.
I am going to be working on a quiet lower body.
I am going to be working to match up the trail forearm with the takeaway plane.
I am going to be working on delivering the club with a trail arm muscular thrust.

Do I need to stop the double overlap grip?

Do I need to move both thumbs on the back side of the shaft, or is it only the lead thumb that is better aft rather than on top?

Thanks in advance for your reply,
Again "Good LucK" in your venture (though I hardly think you need luck, given your substance)