MK1 Golf Clutch 1983

Hello Peeps  I have the above mentioned Golf mk1 GTI 1983 ,the problem I have is a Very heavy clutch, it’s a mk3 20L bottom end, what I need to know is will a 18L clutch do the trick, I have new transmech cs1 clutch and a new cable, the bulk head has a reinforcing plate on it. the gear box is off at the moment and all looks normal from what I can see, 'I’m no mechanic' I just don’t want to put it all back together and have the same problem, I would be Very grateful for any help / comments
 

transmech are euro car parts own brand,i wouldn't fit them…I go for luk or valeo mate
Bert