97' 240SX LE swap for RB25DET!?

[KoukiMongstahh]

Hi I'm looking for some advice or help with the RB25DET conversion into the 1997 240SX LE. I was actually wondering if its smarter to buy the RB25DET + transmission from the R33 to put in instead of the 97'+ S15 motor and transmission (SR20 DET). The SR20DET cost $4600 with transmission and the RB25DET is only $1900 with transmission. I'm pretty sure the specs for both the engines are similar but it makes sense to me to get the cheaper one. Are both the engines installations similar to each other? Also I'm not sure why the price difference is so large when they have the same specs. What I really want to know from anyone who has had experience installing any of these engine, are there any major or difficult issues I will face during the swap or things I will need to modify? Please give me some information about both these engines, pros and cons, which is easier and less cost to do and which requires the least modifications to install. Other than that my brother is a licensed mechanic of 6 years, me and him will be swapping it at the shop but I don't think he's ever went through these specific engines before so it'd be great it we can get some tips for this swap. If there are any other post like this for the 240sx RB25DET swap please post the link in the comments. Also where I will be getting the engine is locally at ----> http://eaglejapanmotor.com/home.php?cat=13
Also please let me know if this guide is the correct one for the SR20DET swap. ----> http://speed.academy/nissan-240sx-sr20d ... de-part-1/
Thank you all, I appreciate greatly for all your help.