For compatibility look at it this way so they made 3.8s FWD, RWD, N/A and SC. So from a manufacturing perspective how could you save the most money making all these? Step 1! Use the same block for all of them that would mean instead of producing say 4 different blocks (RWD N/A, FWD N/A, FWD SC and RWD SC I know they didn't exist it's just a point) they can make one!!! saving on production and design. And from there just think about it. keep everything the same you can and only change what you have to.
it's a basic rule for most engines lol
On a similar note i BELEIVE (could be wrong) all LS series engines have the same external dimensions and the same mounting points on the blocks. MEANING! in THEORY you could place say a 427ci LS7 in the place of the LS1 (assuming the car could handle the addition of abut 300HP lol) it saves GM money because they can produce all the LS engines using identical (or nearly identical) castings and similarly tooled assembly lines which = more money for GM
Yeah this was long I know but I think it's rather thorough should answer most questions lol