On my maxima it waas a breeze. If you have bothe motors out and on stands you should see VERY quickly what needs to be done.
On all L-series there are boss' in the front and in the rear for the oil pick up. If the motor needed front sump then the front boss was machined out and vise versa.
You will need the pan and pick up from the l24e. SOME l28s are already partiall machined for a pick up, some are not. Basically once you locate the front boss, which should be easy, just drill a small pilot hole all the way to the oil gally. then just keep steping up to largeer sized till the correct size hole is achieved. I will see if I can take some pics later.
Once the hole for the oil passage is drilled then you will need to either just bolt up the l24 sump OR if the block does not have the holes predrilled AND tapped you will need to do that. Dome block are already drilled for the bolts but have no threads soma also have threads.
Then of course you will need to block off the old oil pick up hole. I leave that up to you to figure out the best way. I just stick a bolt and washer in it and welded it up.