If it were me I'd do 5 things differently. I'd use the Crane HR224 cam which better matches the auto trans AND the high gearing you prefer, I'd set the compression as I expressed previously, select a different carburetor to better match the auto trans and the unheated intake manifold, install lower gearing (at least 3.50:1) , and use a different torque converter (matched to the gearing and the camshaft).
Depending upon the rev limit I'd select a carburetor rated 600 to 680 cfm or 735 to 780 cfm (when measured using the same criteria used by Holley Carburetors). I'd use the smaller carb if I'm setting the rev limit at 6200 rpm, or the larger carburetor for higher rev limits (6600 or 7200 rpm). The engine blows through a 6200 rpm rev limit too easily with the larger carb, so the smaller carb helps keep the engine under 6200 rpm when that's the rev limit.
The carb differs from the 750 double pumper you mentioned in three ways: its equipped with annular booster venturis, vacuum secondaries, and an electric choke. The annular boosters will atomize the fuel better since the AFD heads can't supply exhaust heat to the intake manifold. The vacuum secondaries are a better match with the automatic trans, the weight of the vehicle … and the gears you've selected. In general vacuum secondaries are a better match for street driven vehicles, providing smoother operation.
600 to 680 carbs
Summit Racing p.n. M08600VS
Demon Carburetors p.n. 1282020VE
QFT SS-680-VS custom ordered with annular booster venturis ($125 extra).
735 to 780 carbs
Summit Racing p.n. M08750VS
Demon Carburetors p.n. 1402020VE
QFT SS-735-VS custom ordered with annular booster venturis ($125 extra).
QFT SS-780-VS custom ordered with annular booster venturis ($125 extra).
Note: The Demon carburetor models I've specified are discontinued but can still be found on eBay and such places.
As far as gears go I'd consider 3.50:1 as the highest gearing I'd use, if high gearing was where my head was at. But something like 3.89:1 will better provide the kind of pep I normally expect.
3.25:1 gears are grandma gears, for slowly driving to church and bingo games (I used to refer to them even worse, but I've mellowed with old age 
). With 3.25:1 gears the 3000 stall converter will never lock-up under normal driving.
If you're concern is fuel economy I've seen lower gearing actually improve the "around town" fuel economy of heavy vehicles. And double pump carburetors are certainly not going to help fuel economy either. If you're concern is turning high rpm while cruising on the turnpike then make sure to have the reciprocating assembly dynamically balanced (aka spin balanced) before you put the engine together. The engine will run smoother, and the rpm its turning becomes a non-issue.
The 3.50:1 gears, a 2500 rpm stall torque converter, the Crane HR224 cam plus a 680, 735 or 780 vacuum secondary carburetor (with annular boosters) makes a nicely balanced performance package that works with the FMX trans.