specifically, if anyone has compared blocks.
i know astron I balance shafts have a different profile to astron II shafts.

My question is (the tp had an astron II head) so when was the astron II brought in? was it tr, tp or earlier?

http://en.wikipedia.org/wiki/Mitsubishi_Astron_engine

sigma started with astrons

different heads and cam shafts as the years passed

the first magna TM -TP to the TR/TS used the same block.....4G54

but different timing covers for chain tensioners ...oil pumps differ tm- tp to tr ts. pistons in the TS dished

the balance shafts are the same from first gen mag till end of 4 cyls of the TR/TS