1) Media blasting is not difficult to do, there are lots of companies that specialize in it. You can buy the bits & pieces to do it yourself, but someone that does it for a living, will know how much pressure to use (to not distort panels) and what type of media to use.
2) A good bodyman will be someone in high demand, whether he works at a local bodyshop or a specialty shop. You want to find someone that has a good reputation and has experience with the type of work you need. I've seen mediocre work from 'reputable' shops & I've had superb work done by someone working out of their garage. Bodywork is bodywork - if someone knows what they're doing & does it right, no judge at a show will be able to tell who did it.
3) Drivetrain: how much experience do you have? Re-building a motor or trans requires a certain amount of specialty tools, how well equipped is your garage? At the least, you'll need an air compresser, engine hoist, engine stand, sockets, wrenches, etc.....You can do it by reading manuals & posting questions on here, but it does require a little mechanical aptitude. There was a long post on here a while back about a guy re-building his tranny & the help he received here was priceless! He got it done & it worked great!
4) Cheaping out on a restoration will only cost you in the end. Take your time and do it right the first time.
5) Recent modern replacement? I don't think Mopar sells 340 bare blocks over the counter any more. If you still have the original repair order and/or dealer paperwork, I don't think it detracts from the value very much. The muscle car market is in a constant state of flux and buyers can sometimes be a fickle bunch and no one really knows where the market is headed. A low mile, original survivor will always bring more money than a restored car. A car with a warranty replaced block? I wish I could pull out my crystal ball & tell you exactly what it would bring, but your best bet is to spend a lot of time going through 'for sale' sections & eBay and see what they normally go for.