Need some clarification please

[bama223]

I have a 2000 Buick century limited with the 3.1 I bought 3.4 upper and lower intake and head's to put on it is it worth the swap 

[55trucker]

There is little to be gained, you won't get the advertised 10 hp difference in the two engines, both heads are the same casting, the intake ports in the LA1 are slightly larger for more top end flow, the LA1 intake valves are so slightly larger in dia (1mm). 

the lower intakes are the same, the uppers are different cosmetically and they are plainly identified by the engine size cast into the plenum.

The only operational difference in the uppers is the dia of the throttle body opening, the LG8 makes use of a 52mm throttle body & the LA1 uses a 56mm throttle body. 

As far as I know the LG8 makes use of the same rear exhaust manifold that the LA1 does, but I'm not completely sure of that.