[vettestr]

Get a new gear reduction starter and then do all the rest of this to make her start no matter what.
We make all of our battery cables from welding lead cable. The use of 1/0 AWG is just over 1/2 OD. but because it has a strand count of over 990/30 it is very flexible and easier to work with than cables from the discount auto parts stores. The ends can be crimp or soldier type but I choose soldier type. Just for looks we use red shrink tubing on positive cable ends as we just buy black cable. Retail cost at a welding supply store is about $4.50 a foot and ends are like a buck fifty each. Seal around cable and cable end with even RTV just to keep moisture from entering under the insulation for years of trouble free service. Use about 3 ground cables works well.
You can purchase starter heat shields but making you own from sheet metal and a large hose clamp is pretty basic. Bend tangs around edges so you can bend under shield all around perimeter with a couple of nuts or spacers taped to body in the middle section, the point is to leave an air gap of less than 1/4 inch between shield and starter body all the way around. Use a hose clamp to secure shield to the starter body and make sure it does not move or hit cable connections. Some sandwich header wrap material between the shield but I find air gap works much better, seems to cool quicker.
Last but not least is be careful with these cheapo plastic battery dis-connect switches as I have found many to leak a little current or have a high resistance from arcing across the switch. A metal Cole Hearsey is an NHRA approved sw. and about 30 bucks and Harbor Freight is 6 bucks on sale. Not picking on H.F. as I use stuff from them but you need to match the performance demand to to listed rating on part. Last but not least AGAIN??? always run redundant ground straps All our controls like MSD box, coils, fuse block,relays et... are mounted on a 1/4" aluminum plate that also is mounted with an air gap for cooling. A 10 AWG ground wire from plate to chassis ensures a good ground. High current items like headlights also have their own ground straps.