All personal choice. A few things to consider:

Is the 253 the original engine?
Is the 253 ready to use? Will cost the same to rebuild either.
Being a HZ 253 it will have a 3.55 diff. That is not good with a 308 TH400, so tyre dependant you will want at least a 3.08.
There are 2 x holes needed in the body for a TH400 speedo cable to do it right.

My advice, not knowing answers to the above would be to use the 308 auto, much better for all-round use. But it depends upon what sort of resto and what you wan't/like.