Combining postage is no problem. The shopping cart system should work but if it doesn't, just purchase the parts you want and I'll refund any additional postage. If you have any queries don't hesitate to send me a message.
For more assistance with watch related questions and general chat, I'd recommend joining the WristSushi forum -
www.wristsushi.com
My blog site is here -
www.vintagetimeaustralia.com