Header identification help and options.

[Detmar]

1970 c10 with a stock 350 (besides the edelbrock 4bbl) when i bought the truck a few weeks ago it came with some headers. PO said they specific for my truck. Truck needs exhaust and I'm wondering if its even worth it to install the headers. I've read with a stock set up there is no gain at all. But I'll eventually put in a gm crate or possibly a 383 stroker. I want a good exhaust and looking at a flowmaster super 44. Or magnaflow. Maybe even something else. Should i install three headers now so it's an easier swap later? Or stick with the stock manifolds. Pipes are 3" and 1 1/2"