The placement of your engine is exactly correct, just like mine. The oil pan used up through '79 is the same as the car pan just like you have it, and it is a snug fit.
I didn't use headers, though, so I cannot speak to that issue.
You may want to consider getting a later oil pan, used in the '80s. It will put the plug further back, over the steering linkage making it cleaner and easier to use.
However, you will have to make several changes, but they are all easy. You will need to change the oil pump and pickup tube because the sump is different. You will also need the main cap bolt that supports the pickup tube. Finally, you will need the external dipstick and dipstick tube that screw into the side of the pan. Here are the parts you will need:
'80s era oil pan
Oil pump
Pickup tube
Cap bolt (and nut)
Dipstick and tube
Here is an E-bay link to the type of pan:
http://cgi.ebay.com/ebaymotors/ws/eBayI ... 0445334235
Hope this helps.