Actually the A block has a lot in common with its EARLIER relation, the Firepower Hemi. So you could say the A/LA block is based on the Firepower.
A smallblock transmission is nearly a direct fit, needs only a little adapter plate stuff. Ask TR Waters.
The motorhome 727 has beefy gts and you may want to put them in a 727 behind a 354, but remember a 354 is the same displacement size as a 360.
R.