I am trying to put together an available equipment list for a game set in October '67 in and around the Mekong Delta.

Was HE and Shot all the grenadiers had; or had parachute and star shells been added?

If the illum rounds are available, were they too long for the XM148?

I am just certain that someone here knows.

I would think yes, but I'm not sure.  The MILSPEC for instance the M675 red smoke round dates at least back to 1969, so I would imagine the 40mm rounds that precede it numerically would be of the same vintage or earlier.  This would include the M583 and M585 illumination rounds and the M651 CS rounds among others.

I'm pretty sure all the 40x46mm rounds with Army Type Designators will fit the M203, so I would assume they would fit the XM148.  The only exceptions that I know of are the M674 CS and M675 red smoke cartridges, which can only be used in the M79, or fired by hand or from the M8 pyrotechnic pistol.