Cos you have seperated the the rear axle from the sierra floor plan you are gonna have problems welding that lot in all square!

if you are not careful it will end up driving like a crab!

Can i suggest taking the time to build a jig that you can bolt the compnents to before welding into the escort body?

Did a rear engine 205 once and built jig that ran under the shell and bolted on to the front subframe mounting points and the same place on the rear subframe/secton that was being welded in the back. As long as the jig is is square (measure the diagonals between pick up points) and you have to assume the original shell is then you will end up with a square car!

Just my two cents!

DC