A great start with your project 374.
A Jung hydraulic pump is a definite must... the 900ml/min shown on this page, I think is not enough flow for 20mm pistons, especially having dual 20's on the boom, you might to change the boom cyls to 18mm. Send these guys an email to see if 1200ml/min pump is available.
http://shop.premacon.com/index.php?cPath=35_80