youre not going to be very competitive with stock suspension... Most cars in SM are thoroughly modified in every respect... suspension, brakes, power, etc...
As for weight, the Bseries motor shouldn't alter your handling too much, it weighs about 60-80 lbs more than your d-series... thats about the same weight as full a/c or power steering... no biggie.
If you want to be competitive in SM, get ready to spend a fair amount of cash... Even if you're a good driver, stock suspension wont cut it unless you live in an area with very few SM cars.
hih