Welcome. Not one of these old fart experts will ever admit it but they all were once in your shoes with their first build. You are way ahead of most of us in that you are asking for advice right off the bat. Most of us plugged along with a dream and only sheer determination or stupidity got our truck running. You will learn a lot and it will help you in ways you never would expect. Good Luck.
Now about your questions: Power! really 250 to 300 hp will scoot that truck right down the road with a couple of ski's behind real fine. There is lots of ways to get that power, your flathead can do it, lots of 6 cyls can do it, almost every V8 can fit the bill. Do you have an urge for a special motor or open to the easy low buck motor? Chev V8 is tried and true and low buck as you can get. Ford small block V8 is a little more work but again easy to do. Building your flathead is points to some, it will cost slightly more than a late model stock V8 to acheive the same horsepower. All this is your choice.
Front end: modified stock will work, Mustang II type is common and will act better on highway. Aftermarket kit that I think is best is Fat Man. Super quality and simple build for you.
Rear end: late model rear on leaf springs is the easiest. 9" Ford can be cruiser or take anything you can throw at it. smaller mustang rear is cheap and will last forever at those powers, S-10 Chevrolet also fits and works great.
A well built mild street rod will do all you are asking. Mine has been Coast to Coast 3 times now and while not show quality or expensive, it sure is fun. Good luck.