Your '89 780 B230FT is likely LH 2.2 (no OBD) with EZ-117K, while the '93 940 B230FT will be LH 2.4 (OBD-I) with EZ-116K. 1989-1991 were engine changeover years for all the Volvo RWDs, spurred on by development of the new 900 series. Even though the 740 B230F NA and 740 B234F 16-valve engines changed to LH 2.4 in 1989, the 700 turbos didn't change to LH 2.4 until the next model year in North America (the reason I didn't buy a new turbo in 1989, but rather went with the all new and similarly powerful 16-valve even though it was not well proven at the time, something many of us quickly realized, including the dealers). OBD(I) was not mandated until 1991 in such places as California and Canada, so Volvo was able to phase in OBD. If both you cars do happen to OBD connectors then you've lucked out with two LH 2.4 enignes and the difference you note might be lack of a "B" diagnostic socket which wasn't used in a 780.

Off the top of my head, you will want everything including the ECU, engine wiring harness, OBD connector, AMM, and as well the ignition system. Best to have the whole donor car sitting beside you. A simpler option may be to pursue just changing the block or head depending on what's wrong with the older engine, probably even simpler still to look for a better LH 2.2 turbo that would be a quick swap, noting whether it's with or without EGR which determines which ECU you use (wiring stays the same). As much as the block didn't change much, a lot of attachments to the block and manifolds did change. Others who have done an LH 2.2 to LH 2.4 swap will know more. You may need to sacrifice the Check Engine light as your unique 780 instrument cluster won't swap. 780s would be much more sought if parts were more available.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now