[Mr.Fixit]

I would recommend against building the engine prior to chassis purchase. You will have a greater understanding of what you want to do with the car after you get the chassis purchased, and decide which options you will run. Besides, the engine you build now might not work well with whichever chassis you later pick. Also, it's easier to spend way too much of your budget on motor pieces, so you may end up with a $15K motor and only $20k to do everything else. The motor is the easiest piece on the car to upgrade later. I would rather see a guy put the money into the chassis and run a stock motor until the budget improves instead of having an awsome motor on a stand and no money left to finish the chassis the way he wants.

For the emissions question....If the car is titled as a 65 lets say, that should be exempt from all emissions testing requirements. It's the date of the motor which determines what year the chassis gets titled as. So you may have a more difficult time getting the car titled with the aftermarket block, but if it is allready titled, than nobody would be the wiser. But I am no lawyer, and I don't work for the DMV so this is mostly speculation.