I just had to replace the engine in my 98 S90, the replacement engine was out of another 98 S90 per my mechanic’s supplier. For the past couple of days I have been doing research to verify that indeed I purchased a 98 S90 engine. After a couple of days trying to educate myself on Volvo coding, I find that very little is out there on the S90. I have found the following cast numbers of the passenger side of the block just under the exhaust manifold, in the #2 / #3 cylinder area, an H followed by a 97 in a circle followed by a 35 in a separate circle. And under the “Volvo” name casting in the #1 cylinder area there is the following number 100153600330 also cast with the block. Is this the block’s serial number? What do the “H”, “97” and “35” mean? If I have miss a past post on this subject, I apologize, I am pretty new at this forum business. Any information you could provide it would be greatly appreciated.