I've researched more about what's necessary to drop a 350 V8 and 350 Turbo transmission in our 57 Chevy Belair, but I have some additional questions.  

I know I will need to get...
1)  Eckler's side motor mount kit (#18-02)
2)  Eckler's rear transmission crossmember kit (#19-153)
3)  Eckler's column shift linkage kit (#19-19)

I'm going to buy a remanufactured motor from a local parts store and need to know what year I should order.  Do I go with something that's in the 1960-1970 era?  I really don't know how they differ from year to year, but I do know I want something with a 4 bolt main.  The parts store told me I might have to order a truck engine because the ones they had listed for cars are all 2 bolt mains.  Any ideas here?

Same question for the tranny.  What year?

Last question...Is there a year motor that would have the bolt holes for both a front mount and side mount motor mount brackets?  It would be nice to be able to mount up the front mount brackets to more easily align the side mount brackets on the front engine crossmember.  Any thoughts here?  

The Eckler's/Classic Chevy kit should have a template you lay over the crossmember to properly place the motor mounts. If not, see if you can borrow a bare block from someone, so you don't have to muscle around 1,000 pounds of engine! Even when GM switch to side motor mounts, the block's still had the front mounts for use in large trucks (we're talking moving van type trucks!).

On the motor, how much do you want to spend? And what parts store are you looking to buy the motor from. There's some advice I can give you on this, but need to know these two important facts.