AFAIK none of the Australian Astron 4G54 heads had jet valves in them (we in Oz drew short straws on a lot of cars and options that seem readily available elsewhere in the world) . My knowledge on the Astron engines is on the lean side. Only option for getting your hands on the M27 might be to make friends with some mental Australian guys and have them source them from wrecking yards and freight one to you. I have a mate whose knowledge on the 4G54 is monolithic (he is a huge Mitsu fiend and owns a modded EFI GK Sigma, a GH Sigma turbo and a factory optioned GSR Sigma) so if I really needed info he would definitely be the guy to speak to.