The 360 bell will fit the 273, use the 10.5 flywheel (130 tooth) as said by MOPAROFFICIAL.
The larger bell MAY have a couple of interference points in an early A, mainly at the firewall/floor seam. Not everybody experiences this. If so, fold/beat the seam flat in the offending area(s). Brewer's sells a hybrid linkage to fit the later bell in an early A body.
If swapping from an automatic, make sure your crank is drilled for a pilot bushing.
