[Aussie Mike]

Others may disagree with me but I'd go with the stiffer chassis. The LS motors are very light which will balance out any extra weight in the chassis.

You have to remember the performance potential of these motors compared to the older standard 5.0 falcon motors usually used in MK1s. A hot windsor 5.0 will probably be making around 160-170KW at the rear wheels where a stock L76 will probably be making 220KW at the wheels. Over 300KW at the wheels is possible with just a change of cam and a good tune. The LS series motors are making big block power levels and probably need the chassis to match.