New guy,truck story and questions.

[FordFighter]

Got a 70 3/4 here,paid 2000 and drove 300 miles to get it.Drove it home,smooth 55MPH truck,got it home and pulled the front drums,they were so bad I went to the junkyard and pulled drums off another,had em turned and put new shoes on,better,grind gone.The 350 had a good oil leak goin so I raised the engine an inch and a half and dropped the pan,new gaskets for pan, timing cover and crank,leak gone...Good Workhorse,has proven it's worth....Now,I see a 300 dollar 250 I6 on the web....looks clean...owner said strong runner...would a swap make a difference? If I buy this engine and take the time to bolt it up to the 350 tranny under there....is the torque and fuel economy going to be worth my frustration and sweat?What else can I say? The trucks *****en,I love it...I drive easy and I don't give a **** about speed,but I would like to get get a few more miles a gallon out of it without sacrificing it's ability to pull my trailer under load and sag the coils from time to time.Any takers?