CALVIN - I'll try to answer some of your questions.
A K341, 16 HP will have ten head bolts or studs. A K301, 321, & 241 will have only nine. A K241 should have a flat bottom oil pan, and a K301 should have a sump or deep oil pan. A K321 should have the large flywheel and blower housing requiring either a WF chassis or the flared out section in the frame to clear the wider blower housing. But I know there's several NF CC's around with small flywheel K321's in them, like the one out in my shop.
Replacement engines were much more common that you might think. Back in the 1960's & 1970's when Dad was still farming most IH dealers had a complete K241 sitting on their parts counters as a display item, with a $300-350 price tag on them. The K301 & 321's not so common, they wouldn't set level with the deep sump oil pan. In 1981 I bought a complete K241 direct from IH's Kohler sales representative for $300 picked up at his house in rural Sheboygan, WI, at the time it was over $500 at an IH dealer.
The '65 vintage CC 70 out in my shop now was professionally rebuilt in 1968, Dad & I rebuilt it again in 1971, and the K161 was replaced with a complete K181 in about 1974 or '75. So within ten yrs the engine was replaced.
A complete replacement engine had all the shrouds included, along with a new serial number, and corresponding spec number. Kohler & IH also offered "short blocks" which was a new block, crankshaft, rod & piston/rings, etc but no head and no oil pan I think, it's explained in the Kohler K-series service manual. Also a "mini-block" was available with the head & oil pan. And with both those types of service replacement engines the old shrouds from the tractor/engine were reused which meant the serial number and spec number were probably not correct.
The bigger engines did last longer than the tiny K161's & 181's. They really struggled to run the 38" decks. But the K241 & 301's lasted much longer. But I'd really be surprised if there's many 10, 12, 14, or 16 HP engines that haven't been rebuilt or replaced by now.
The K-series Kohlers are what's known as a "parent Bore engine", with no replaceable cylinder sleeve or "JUG" as in a piston air cooled airplane engine. You bore & hone the bore out.010", .020", then .030" and install corresponding oversize pistons & rings. The O/S pistons are moarked 010, 020, 030 to their top surfaces.
Most farmers were pretty capable of significant repairs, removing & replacing a complete engine was maybe a two hour job with just hand tools, rebuilding the engine required a lot of specialized machine tools to bore/hone, resurface valves & seats and by the time you bought all the parts & labor the cost of a rebuild really wasn't that much cheaper than a new engine of one form or another.
Since here in a few months the 50th anniversary of the production of the First CC will be celebrated, and many of these little tractors have passed thru MANY many hands, it's impossible to tell what all has been done to them since they were built. I'm just happy when mine start and run well in their current configuration. I remember a discussion here many years ago where someone bought a brand new, never sold 982 with all the options from a dealer down south, Texas, Arkansas, Nebraska, etc.... The tractor had sat on the dealer's showroom floor since the day it was taken out of the shipping crate back in 1980,'81. And yes, it was never disclosed what that tractor sold for but I suspect it was much more than the 1980 Mfg's suggested retail price.
