here is a picture of my boat ass. can be seen that my transom and the drive are 4" to 6" inside of the hull end.I have a few questions.
1. what do you experts can say about this hull, transom shape? (deadrise angle,strake,reverse chine)
2. am I get any gain in handling and speed if I put extension box,like this http://www.offshoreonly.com/forums/s...ing-arms.html?
If I understand correctly, this box would increased drive height, and reduced x dimension between the bottom and propshaft, am I right?

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Leave it alone. Buy a boat intended to go fast.

That ^^^^ and you don't have the clearances for a raised drive. It is going to hit the underside of your swim platform more than likely.

and its a 19 ft boat if I stand correct --- IMO it could have the possibility of hurting performance. Moving up and 12 inches back on such a short hull

I thought about putting a land and sea stern jack on mine. Never considered using a bravo.
Having experienced 2 of those boats over 10 years time ,im thinking your going to regret not putting a volvo dp drive on it with cast aluminum manifolds going through the prop.

I don*t want triple digit boat
I want to squeeze 80mph from this hull.
here is the video from this boat doing 75mph
https://www.youtube.com/watch?v=0zWRDPNYadw

I had a '91 185 Searay that did a legit 75 and I achieved that with 435hp and an Alpha SS drive. If I would have gone to a bravo, I probably would have lost 5-10 mph and maybe gained a couple putting a shorty imco on it. What's wrong with more power? Are you starting to get to some instability. The SS drive took care of that for me, but good luck finding one.

Looks pretty stable at speed, be careful what ya ask for and don't be that Donzi guy @ LOTO

It has a nice set to it as it is..... start screwing around with the center of gravity and such and you might lose that.

It would be easier to just add a bit more power to get that extra 5 mph

Exactly the COB and COG very easy to change and or screw up in a 19 ft boat - Like I said possible hurt performance and add handling in the mix on top of.