Re: lighter motor - want stock ride height
This is rough, but I'd use the "spring rate" method,..for instance, take a stock height front spring with a spring rate of 300 lbs. It would take 300 lbs to compress the spring one inch. There are two springs sharing the load and since the engine weight is somewhat rear the two coil springs, the rear suspension is less burdened with the aluminum engine and the rear would ride slightly higher.
So, I think your front end height would only be reduced by 1/8 inch or so with the 100 lbs reduction in engine weight.