Coolant Change Ford Dover

[Phil23]

I have a 4 cylinder Ford Dover with a Lees Marginalization (New Zealand) which is exactly the same short block as used by Lehman and very similar Coolant system.
My query is what % should my coolant Sg be, I am currently at about 30% but thought it should be higher???
I wish to change my fluid so as to know where I am from a specific date/hours, how is the best way to get it out I cannot find any valve/tap on the block like my old D series had. Thanks in advance

 

[BeeJay]

Lee’s manual recommends 50 % . The drain tap is on intake side of the engine, below the manifold on the side of the block. About level with the back of the alternator.