You can't do it in a backyard unless you buy a new shortblock or long block and just install your intake and/or heads on the new block, pull the old motor, then stick the new one in.
I have heard some conflicting things about 347 power. If you use all stock parts, you may not gain much power, but you will add a lot of low end torque. If you have a proper set of heads, cam and intake, you will gain a lot.
I would budget a minimum of $2500 for this project. You might be able to do it cheaper, but that will either be from using cheap parts, doing some of the work yourself, or luck.
It's about 8-900 for the really cheap 347 kits on ebay, then you have to either put your car out of service for weeks, or buy a donor motor. $500+ for a bore and hone, deck the block, ballence job and hanging the pistons. Then there are the little things, timing chains, bolts, gaskets, oil pan and pump, they all add up.
If you don't want to take any chances with how those things add up, just get a shortblock from ford. They are pretty cheap and it's a no brainer.
When I look at those prices and what you get, I would rather spend 4-5k and get everything forged in a race block. It can be done with top shelf parts if you bargain hunt and take your time. I just got some $1,000 Lunati rods for $500 through Ebay. I'm now looking for pistons and a crank.
I'm waiting for World products to start making their WindsorR race block. It's suposed to be out by the end of april for about $1500. That's a good deal when a sportsman is rated for only 600hp at $800+ and the Dart's are over $2,000.
That will leave me with $3000 for my crank, pistons and oil system. I think I'll be able to scrounge that for less, but I don't expect to have my engine done before 2005.
My question is what is the cost involved in this and also how hard? could a couple of weekend mechanics 
like me and my friend do the job in the backyard with some patience and the right tools? How much power would I be looking to gain with the change? Any info would be helpful. Thanks 
