Which Starters & Shifter Linkage?

I assume you are saying it is factory floor shift automatic. If so, factory floor shift linkage for your body style with 727 will fit on a big block 727 if it has the all correct mounting ears in tact on the case.
What B-body headers are you planning use? Most good B-body headers, such as Hooker Comp or Supercomp, will not fit the small A-body engine compartment. TTI A-body headers will allow the use of any factory-style Nippondenso based starter, from parts store replacements, to Mopar, to aftermarket.