This may seem like a dumb question, but I put the wire looms on my 350 and now I need to add length to my plug wires. I measured the length to the furthest plug and it does not seem like the custom fits will be long enough. Should I buy wires for a BB or am I doing something wrong?

aftermarket wire looms dont follow the way the MFG routed the wires.
you should have gotten a universal kit (gives you a bit more lenght )
also if you order wires that are for under header installation they are a bit longer aswell.

Best bet is to buy a a quality universal fit wire set. I like Taylor. Be sure to get the crimping tool to properly install the distributor end terminals.

Somewhere on this board is a pictoral I did on crimping the terminals, if anyone can find it, I'd love to add it to the electrical basics sticky!

In general, for those installing pre-cut wires I do the following. I number all the wires as I remove them from the vehicle. Then I hold them all up straight. I pick either the longest or the shortest (depending on my mood and what I have left) and pick the respective longest or shortest of the new wires. I install that new wire in the appropriate position and repeat the process until all the wires are gone or I have two or more left of the same length.