looks like a good engine stamp ,
Seller does not disclose if frame matches , or did i miss that ?
Triumph introduced a new system of numbering engines and frames.
There are two letters ... a five digit number... and a model designation.
The first letter represents the month,
the second the model year,
numbers for each year start at 00100
model years are approximate ,
with production starting sometime in August and running through July
G is for june
C is for 1969 and 20,000 seems a fair number of a june t120 engine ? ,
considering Triumph was producing around 900 bikes a week
and make over 40,000 bikes in 1969 .