I'm sorry I need to correct some of what I wrote above.
You DO have a 977L, although it's an early one that is still fitted with a D333 model engine (this was before the introduction of the 3306 engine). The 70J-prefix started production in Japan in 1967 as the 977K model, and it was re-badged as a 977L starting in 1971.
When it comes to 977L the 11K-prefix of US-built machine is the equivalent of the 70J Japanese machine. As regards equivalence there are certain updates that give machine Serial Numbers. For example the horsepower increase of the D333 engine to 190 FWHP occured in 1971 at 70J1303 and 11K3919 to coincide with the introduction of the 977L model badging.
The D333 engine which you have in your machine was replaced by a 3306 at 11K5083, so I suggest that you use a Serial number somewhere above 11K3919, probably about 11K4700 or thereabouts. It ought to be pretty much the same in most respects as your 70J1637.
If you want to make things easier you could get hold of a Parts Manual specifically for the 70J machine. UMX00191 is what you need. It covers 70J machines from first built to 2222. Here's a link to one on
eBay for $50. New (still available BTW) the same book is $150.
