[AZFA20]

Dimensionally the LSx series engines (block, heads, basically the actual engine) are all identical in size. The differences arise in regard to dimensional fitment due to variances in the intake manifolds and accessory placement (alternator, style of water pump used, AC compressor). The LS1 for instance has an intake manifold with minor but significant differences in design that change fitment clearances compared to the LS3. The truck intakes have obvious dimensional and design differences. All of them will fit but it's just a matter of final placement. The engine bays in the 86 are giant to say the least thanks to the enormously wide FA20.

The transmissions don't really matter as far as which variant of Tremec T56 series that is used. There are however, pros and cons to the different variants so for instance the Magnum XL that was mentioned is no different from any of the other Magnums other than it is XL (extra long). What this does is just houses the extended shifter placement internally resulting in a slightly better shifter feel than a standard Magnum using external shifter linkages to relocate the shifter. Any of them can be adapted to change shifter placement but the Magnum XL just happens to get the shifter to the OEM provision without using shifter extenders. This is also assuming your mounts have the engine placed appropriately for the XL. Vorshlag has designed their mounts to best work with the XL but not a requirement whereas Weapons Grade uses a standard T56 non magnum variant.