WTF is an Interstate MT-58??

If it was me, i'd go overkill on buying the battery...... batteries approved for diesels are the best - pushin 300+ lbs compression at 20:1 compression ratio.

If it doesnt fit your existing battery tray, you can *make*it fit - so go ahead and buy a true gorrilla battery. The ballsiest battery conversion I've ever seen is Sears Automotive batteries going nto Moto Guzzi motorcycles, replacing typically pitiful 12volt M/C batteries..... a very common conversion that just barely fits underneath the seat after bending the sheetmetal battery tray.

Basically, you can never put too much battery in any vehicle. They are rated in amp/hours, i think.