Can someone tell me engine harness differences?

[ts71281]

Ok, my truck was originally a 307 3 speed manual truck but has since been converted to a 454 with a 4 speed muncie. It's time to replace the engine harness since it's in really rough shape. What's the difference between a smallblock v8 engine harness and a big block v8 engine harness? I am going to order one or the other but even the customer support lines at AAW or MH electrical cannot tell me the difference. Also, is it worth the 8 week backorder from MH or just order immediatly from AAW? Thanks in advance guys.