Up grading to a V-8 would require changing the "K" frame. This is not difficult, just expensive. There is a "K" frame for the 6 in a row, another for the smallblock, 273, 318, 340 and 360 cu in and another for the big block, 383, 400 and 440 cu in. It all depends on how fat your wallet is.
That would be the 5.7L / 350 Vortec.
Look in your owner's manual.
12lts
RearRear
under the left side of the dash around where the hood release latch is.
8.15 -15"
Your Starter is located at the front of the engine near the transmission. You need to take off two wires running to the starter and then two bolts holding it on. It's very easy.
There are no 2 rear doors.
is it a 2door or 4 door ?
A base 2 dr. dart in 1966 was about $2,500.
The hood ornament should be the flying jet enblem.
Dealer would have to run VIN ( vehicel id number)