Quick 1970's Ford truck question

[tuna.Rc]

It's around midnight, I got a call for a vehicle I'm selling. A guy offered me a trade for my car, not sure if I wanna pass it up.

The truck is 1976 Ford F100 4x4.. It had a 390 V8 , it still has auto trans/t-case. Im assuming a C6 and NP208 .
My question is , Will a 1978/1979 300 Inline six bolt up to the C6 using a 300 I6 bell housing ? IF so , would I use the 390 or I6 torque converter ?

The old lady said I can do it, but as long as I can get most of the parts lined up before I get it. We are moving in to another house , and she dont want me having 2 project vehicles sitting outside . 1 is cool,but I'm pushing my luck with 2 ... and all my rc cars

[RC10th]

Is the 390 going in something else like a mustang or are you converting the 100 to be more fuel efficient?

[tuna.Rc]

Is the 390 going in something else like a mustang or are you converting the 100 to be more fuel efficient?

The truck had a 390 . I found a "390 V8 " on craigslist , got the numbers, turns out it's a 1968 427 side oiler.That one needs a upper rebuild. I had a few of these trucks that had 300 I6 's , and the gas mileage was great, but they were all factory built non emissions engines. Might as well rebuild a straight six and put it in.

From the research I did last night, that 427 is a rare engine Might pick it up just to have it