The short easy answer for the engine is to set up your carbs to run E85. This stuff is good to 12.5:1 and is cheaper than premium. Now compression worries are a thing of the past. don't bother with the water injection. Go to
www.raceonE85.com for details. But if you really really got to have water injection, I'd go with snow performance. Their water/methanol kits are professional and work. My brother has one on his blown 55 chevy.
They make adaptor kits to put the 6 speed behind a small block chevy, that's all you need to put it behind your 250.
Wilwood makes an inexpensive universal pull-type slave cylinder. I use it on my mustang with no problems. If you can build a car from scratch, you can probably build a simple bracket for it on your bellhousing.
Centerforce would be the light clutch you are looking for, and should handle that horsepower level.
And last, if you put a 300hp engine in a 2000lb car, your old lady driving days are over!
On second thought, you should just sell me that engine and get a stock one. Then you wouldn't have worry about all that unneeded extra horsepower
