Ok Daves got back to me & he has weighed the bare L18 block w/ maincaps at 37kg. CA18de w/ sump no main caps 39kg, 2.5kg for sump makes 36.5kg add maincaps & wala! 37.5kg....wait forgot ca18de ladder brace is about the weight of sump!. On even par would be the weight of a ca18 vs L18 as both have non full c-weighed cranks so the 5kg heavier l18 could be from the older heavy starter & beefier crank as far as I can muster?.

Edit:
Lags, only issue is the "L" is wider than CAs so dont have an L to see clearances in this part. However the Z18ET head is 11.8cm tall exactly & block is 20.71cm from crank centre to deck height (20.51 CA) yet the skirt & sump combo on L series is less than the CA with deeper sump due to longer stroke by -1cm. L and CA-DE heads are much taller about 18cm for the L from memory (DE Nick will know). However you should have a CA for your 1k to compete with the SR in your 1600 to see which is more fun :))
Ive got a ca16de block (plenty of meat for 84mm slugs) for a DET engineering capable setup and the L/Z will need to be an L16 for starters (will need dry sleeves).

As for me scone it turns off really well round the inlaws ;)