Please post a picture. I feel I had a Ward's with a lime green cast iron case in the 70s. Did John Deere build tillers? Loger

I have a tiller very similar to the one you are describing. I inherited it from my Grand father. The tiller has the word Turfman 3.5 on the front of the steel housing with that same lime green color you are describing. It has a Briggs 3.5 that is painted white from the factory.

I have one as well I brought home from an old tool shed. I ordered a standard 3.5 horse pulseprime kit (carb, diaphragm, governor, & tank) from partsdirect.com instead of trying to replace a bad diaphragm and clean out the dirty gas tank.
It fit perfect. The throttle cable was also replaced. I first bought a regular throttle cable made for a lawn mower, but it kept working loose on the frame and the cable fell loose from the control switch. I found an Edelbrock throttle at Autozone and it fit in the hole on top of the handle and has stayed secure. Rather than cuttung the cable case and and the cable, I wrapped the excess cable around the handle frame twice. It fired up on the second try. I can get you the pulseprime part # if needed, $85. The throttle was $17. Still cheaper than a new tiller.

That tiller sounds a lot like one I bought back in the 1980's. It was an old tiller then. It had a 3 or 3.5 hp Briggs on it. The engine mount would slide back and forth on 4 shoulder bolts to give forward and reverse. It was a very simple and trouble-free design. I would like to have one like it now.