You need to ask yourself 3 questions: 1) What engine to use
2) What powerband you desire
3) What is the desired power potential of the turbo (on pump gas)
This will narrow your results down to maybe 5 turbos. You then build your motor accordingly, most likely sleeving, forging, and carefully tuning with larger injectors, Hondata, Chrome, etc. and don't forget drivetrain upgrades (i.e. clutch, pressure plate, axles, and please get some good reinforcement to support the added power.) Of course, you only do these things if it's in your budget.
I'd personally use an LS block. It's cheap. Do LS/Vtec. Buy the cores (head, block, tranny) from a salvage yard and have them built to your standards, which should probably be atleast nice pistons, rods, block guard, and a good valve train. Buy all custom drivetrain, with a good clutch. Buy the HASports motor mounts (and shift linkage if you need it).
Remember, powerband is important for your type of driving. You don't always have the faster car because you have more PEAK horsepower. It's sometimes better to have a good broad torque band than to have it all at the top, especially if your into road racing. On the contrary, I personally believe that peak torque and power are important to take advantage of gear reductions in those nice 4.9 final drive trannies. Therefore I would use a B16 hands down. Plus you can utilize more power because your not burning the rubber of the wheels from a dig or slow roll. It CAN be just as effective to have 200ft/tq at 7000RPM's as it is to have 300ft/tq at 4000RPM's. JMO though.
Two things should influence what engine to use: your powerband desired and of course your budget. You CAN make strong mid range power out of a B16, but it's hard to do, and you'll have to sacrifice some top end, which makes it harder to achieve 300whp. Using a larger displacement motor will make both mid-range power and 300whp easier to achieve, only it might cost you some traction and extra money.
Once you've answered these questions, your options will be down to a few. Call up Rev-Hard, Drag, Full-Race, and tell them these desired assets to your setup and they can help you fine tune your decision for the parts, turbo kit, and about how much boost to make.
my .2 cents, peace.