First time poster here. I have an '84 vanagon with a EJ25 SOHC engine and transaxle. The engine needs to be replaced after it seized up due to an oil pump issue and I have a couple questions. 

1. Do I need to use the same year and model of Subaru engine that is in the van (a 2000 Legacy) or can it come from a newer model/make? 

2. What are the advantages/disadvantages of replacing the EJ25 with an EJ20?

Thanks!