I have a new radiator which I fitted but I'm not that sure I have fitted it correctly. Here is what I have done.
Drained the system from radiator and middle pipes underneath - removed the old radiator - couldn't find the engine block drain (In reading up I have heard that is not essential to open anyway) -I elevated the car nearly a meter at the back - more coolant came out - then I got the hose and flushed the system with water till it ran clear - filled it with water and bled it - put in special system cleaner - ran it for 20 minutes - drained it again - filled with coolant and bled.
That all seems ok but I can only get 5 to 6 litres in? Its a non turbo what am I doing wrong? I thought it should take 13 litres?

Bleeding the system takes a lot of patience. Search the forum on how to properly do it. It takes about 13.7 lts I think from memory.

As said, be patient as I have just lunched an engine do to poor coolant bleeding. Also make sure your heater is open and flowing for when your bleeding to get all the coolant.

Proper bleeding is very important with MR2's!!
If you want a comprehensive article on bleeding, PM me with your email address and I will send it to you.
(It's a PDF too large to PM) 
 
About that 13 liters the system is supposed to hold.
After completely draining my system, I can only get about 8-9 liters back in.
There is over a liter in the overflow bottle, and probably over 4 liters still in the block/water pump/bypass circuit on an NA that won't drain out.
I have checked 2 different Gen 2 3SGE motors, and they definitely don't have a block drain tap, even though the manual says they do.