Geezer,
'83's had both T-5 and SROD 5 speeds, and they have different bellhousings so you'll need to get a 5.0 T-5 bellhousing with your tranny from the V-6. This is a paragraph from a discussion on upgrading a V-8 into a Fox Body Mustang:
Bellhousing: This depends on the transmission your are using but the 4 basic ones are the standard transmission bellhousing for a T5, standard transmission for the SROD or Toploader 4-speed, the auto bellhousing for a C4, and the auto bellhousing for the AOD. Other combos are different still such as the Tremec. The best way is to get the bellhousing with the tranny if possible.