Welcome to the forum, and looking forward to watching your project get done.

I'd say it depends on what your end goal is for the truck. If you really want a restored original, good for putting around town or running in on Saturday night for an ice cream, maybe making a run to the hardware store or lumber yard but limited to around 50 to 60mph on the highway then restore the 216. If you're wanting a hot rod, suitable for driving at modern highway speeds safely and going to distant cruises and shows then you're looking at the 400 engine, new tranny, driveshaft and rear end, along with upgrading the brakes as you go. The key to a good project is to go into it with a good, detailed plan; and the budget to support it, either doing the bulk of the work yourself or writing checks. Add to that the schedule to get it done and you're ready to rumble! Just my $0.02, in my second project now, slooooowly.