again i'm not too good with engine prices but i do know that the V8 2UZ-FE shoudln't be too expensive since it is not a high demand engine (most people want a diesel 4.2L)
depending on gearing i'll say 0-62mph in around 6 seconds since there is alot of weight to be moved (and that is pretty fast for a car over here) not sure about 1/4 mile times but it shoudl be close to the times of the LS430 since the power to weight ratio is about the same.
if you already have a 2JZ-GE in it (approx 230hp) why not go for a twin turbo stup from a supra (2JZ-GTE) using CT12B (ceraminc) turbines or for more power go for the CT20A Stainess steel ones. I should point out that you'll need forger pistons and connecting rods as well as possibly having to change your valve springs for slightly harder ones (all parts can be sourced from a stripped GTE engine)
You'd have to increase fueling for the TT aplication and woudl need approx 500cc/min injectors and an intercooler.
All in all you'd achieve approx 280-320hp and still have your original engine in the car (better weight distribution when compared to a V8 swap, but the sound of a V8 is something else!
as for the CNG,... ROTFLMAO!!