Have you done anything to your rotavator yet? I had mine out today for the first time since last year, started first pull and ran perfectly, mine is a 350 with a K141 but any Kohler engine is way better than a briggs and scrapum.
Some of what Clodhopper told you is incorrect, parts are easily available there are still a couple of places that specialise in Howard rotavators and you can get head gaskets off ebay with a quick search.
The head should come off easy, I can't imagine the bolts would be corroded unless it's been left outside for a long time.
It's a side valve engine with the valves in the block so you don't have to worry about disturbing the valves and once you have the head off pull the starter cord slowly and have a look at the valve seats if they look half decent I would leave them alone as getting the valves out, reseating them, then re-setting the clearance is a lot of fiddle.
Just give the head and block faces a clean, check there are no nasty scores or major wear in the bore, stick your new gasket on and slap the head back on
The oil seals on the rotor shaft are two lip seals back to back I believe, the seals are mounted in the housings bolted to the chaincase with half a dozen little 7/16" head set pins the heads usually get worn away by the soil so may be difficult to get a grip on and you might need new ones.
The reason the seals go is because some people seem to leave string and wire lying in the ground and it gets wrapped round the rotor shaft
The 300/350 is still the best, user friendly, perfect sized rotavator ever made and if yours is restored to good nick would be worth £300+
One thing I have done with mine is convert it to electronic ignition, which does away with the points and condenser, like this one - eBay item number: 322502880161
Kev
