52GMC6 has covered pretty much all the differences, I can only add that the blocks have different casting numbers (See
Inliners) and all internals and cylinder heads are the same as civilian versions. Military blocks are rumored to be stronger castings but I've had both apart and side-by side, the only differences other than those mentioned above, are that the military block has some additional webbing where some of the accessories are mounted. The compressor mounts are great for supporting a power steering pump or A/C bracketry. And the double groove damper works fine if you move the radiator to the outside flange of the core support. Just be sure to use a water pump from a 270 to match the wide belt size. Some clearancing of damper pulley may be needed to clear the front engine mount if the pickup center mount is used.
