Piece together or complete
My opinion after spending way too long on my swap is do whatever will get you on the road faster. If for you that means getting a turn key package, then go with the connect & cruise - less fussing on computer/wiring/tune and there's plenty of work remaining to get it in the car anyway. This assumes the tunnel work for the 6L80E is just a matter of cutting further and not running into some major obstacle in the Dart.
With regards to rear gearing, it depends significantly the tire size. In my Nova I have 275/35R18 with 3.73s and Magnum-F 0.64 overdrive ratio. I am turning about 2,200 at 70mph in 6th gear. I recently did a 300mi trip down to Corona and back, mostly freeway but with some stop and go traffic and I averaged 18.7mpg.My 370 made 415rwhp through the old TH400 - not sure how the crank HP would compare to what you're working on, but 20mpg should be very doable at that power level with a lockup converter OD trans (either 4L80 or 6L80).
The L92's had small cams installed along with better valve springs and push rods installed. On the chassis dyno they made 420 rwhp.
If are thinking some type of power adder I would I would plan ahead engine wise. Do you need forged internals? Lower compression?
Good luck with your project.







