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I would focus more on gears, suspension, and tires than on an engine for a trail riding. If you are going to run the Lincoln 302 stock, you could can buy a Ranger with a 4.0 SOHC motor and have the same power without the cost of an engine swap, although if you find a 4.0 with an auto you'll have a crappy transmission. If you are going to build the motor up some, I wouldn't start with a speed density motor from the Lincoln, especially not for $1800.
Here are the prices and a small list of parts you can use... seems obvious to me
$1800 - Lincoln with a speed density motor, and a 2wd AOD.
$1800 or less - Explorer with a 5.0, a 4 wheel drive 4R70W (better than an AOD and doesn't need the output shaft switched!), radiator, FEAD, wiring harness, fuel lines, 8.8" 31 spline rear end with disk brakes. The A/C is easy to use also. Then you can sell the AWD t-case and front differential from the Explorer to buy a t-case for your Ranger.
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