Eibachs are not bad at all for street, the stifness also depends on the choice of shocks, I have adjustable konis, and at hardest point, you can´t go faster than 5mph over a speed bump!
Of course if you want to go out on race track, I would have said to get coil overs.
About the engine, Downing atlanta has stopped production of the kit for the M42/M44. because eaton doesn´t build that supercharger anymore.
And about stroking/boring, there´s not really much research to do, just bore the block, and dump the new pistons in. Stroker crank? just take the stock off, put the new one in, and look for piston to valve clearance.
When you have that much money to spend on a car, you can´t just buy a lot of cheap mods hoping to end up with +10hp, and a stiffer chassis.
Do a research around, and depending what mods you are willing to do to your car, chose one route or another.
That´s just my 2 cents there.