Any horizontal engine is easily adaptable, especially on an application like a tiller. One important spec would be crankshaft diameter, so you can use existing pullies. Muffler and cables are easily modified, so not too much of a concern. On the engine ID plate are SPEC/TYPE numbers, you can always call with that info to see if they offer an exact replacement. I know Honda offers replacement engines for many applications. Also check Ebay, many H series on there for sale.

Try northern Tool. They sell all kinds of engines

http://www.northerntool.com/webapp/wcs/stores/servlet/category2_6970_76

Thanks guys, it looks like SEW has the best prices. I might go with a Briggs Intek engine if it is compatible instead of the Tecumseh.

Some tiller manufacturers use a hole in the crankcase for the tiller reverse, as well as a 1/2" pto shaft. The Intek is a nice choice if you don't need the above specs.

I was thinking exactly the same thing since I don't need those extras. In fact I ended up ordering a 10 hp Briggs Intek from SEW, model 204412-0125-FT with the spacer plate. Only problem is the engine says "Troy Bilt" on the side.

Let's see, the tractor, tiller, and compost grinder are Roto-Hoe, the engine will say "Troy Bilt", and the snow blower attachment is a Simplicity. Just call it Frankentractor. A tribute to my late dad's ingenuity.

This will be the 4th engine on this well-used old circa 1979 Roto-Hoe.