You are correct. EJ is engine family, a la EG and EZ (my stolen car was an EZ30D, an EZ30D first gen, the "H6-3.0" with badge that said as such. Great engine. An SVX is an EG33 I want one of those too but that's down the road.)
EJ201 = 2.0L
EJ251 = 2.5L
I have not memorized the bores and strokes but you are correct on displacement. I think 82mm or 92mm bore and 68mm stroke but don't quote me on that.
The ECU does not need to be reprogrammed or anything like that it's basically a direct replacement the ej25 is really just a half liter bigger ej20
And half the JDM slot videos I saw have them drilling a hole for the cam sensor in the block somewhere and half of them don't just have them checking the pulleys inside the engine (or something like that) and one shows an easy way to change the flexplate (Auto is flexplate, manual is flywheel, yes?) by taking one bolt off of the time because the USDM one is bigger than the JDM one and then the holes will line up
But since it's a EJ to a EJ I think the ECU doesn't need to be changed at all
Almost went with a cammed motor and my mechanic told me he guaranteed me it wouldn't run right.
Here is a link to the motor that did not go in.
<p>140k mile shortblock pulled from 01 Legacy GT</p><p>ported/polished SOHC heads</p><p>Delta 2000 cams</p><p>Supertech springs/retainers</p><p>Intake manifold painted red</p><p>Head gaskets, valve cover gaskets, and timing belt+water pump have 5k miles on them </p><br><p>Will come with...
and I do apologize but I don't have time to link the JDM motor that I bought at the moment because I'm switching charging stations on a forklift but it's from a JDM engine site.
EDIT: Only took short time. Here is engine.
Buy Subaru Legacy 1999-2005 JDM Replacement For 2.5L Engine - EJ20 Sohc 2.0L for only $1049 at Low Mile JDM!
It is a drop-in replacement.