I just went through something similar.. I rewired the heavy and light wires to the starter, the fender solenoid is low amp, try putting a screwdriver between the two poles on the 2nd starter-side solenoid (consider not having your arm in there) someone said it was 2 gauge for the main, I used 12 for the secondary. you should only use thin strand wire as it handles the movement without breaking.. I used compression lugs from Home Depot (electrical section, usually used for home fuse/breaker panels) heat shrinked the connections to keep out water.
I also replaced the positive wire to the fender relay, as this runs the whole electrical system since the fuse block is wired to it as well (used remaining heavy wire)
good time to check grounds as well, ground wire battery to frame/ ground wire from firewall to back of engine.. mine were very brittle (bare wire/woven ribbon type)
so all in, if you do all of it, 8ish lugs for 2 gauge, at least 2 smaller lugs for the 10-12 gauge solenoid wire. I did mine with about 15 ft of heavy wire, and you'll need almost as much for the solenoid wire (it runs with the heavy one back towards firewall/ across the bottom of the truck (might want to rewire over the motor if you off road)
I cleaned up all my connections at the battery with lugs to make it look cleaner, but you'll definitely need a new battery connector (I used the clamp type, using the bolts of the clamp to hold the compression lugs) Consider also if you do reroute, get some appropriate sized plastic wrap/shielding to keep down abbrasion. don't forget the zipties!
watch the exhaust manifold, try and keep the wires as clear as possible, as it will get you back into this situation real quick!