New to me 1998 Bigfoot M-30-C-10.3

There a a few of the not so expensive converters that will work with GEL.

Progressive dynamics which is great has a special remote control for GEL..

The 9100 series Progressive dynamics converters coupled with the controller/Wizard will do it for you...
If you later decide to go with AGM or Flooded Wet cells then you just purchase the other controller/wizard...Cheap!

http://progressivedyn.com/prod_details/charge_wizard_9105gv.html

So I would contact Randy at Bestconverter and talk to him..

As a note, the package size of the 9145 is different than the 9160...
If you already have the Magnetek 6xxx converter the 9130,40,45 will not quite fit in there, the 9160 will....

http://www.bestconverter.com/9100-Series-Deck-Mount_c_39.html

Here's Bestconverters link for the conversion:

http://www.bestconverter.com/MagnetekParallax-to-PDI-or-Iota_ep_13-1.html

Great writeup for the actual conversion... You will need to run way heavier wires from the converter to the battery (s)... Another thread for this or some searching will provide you with your needs.