The conversion to from Lovibond to EBC is times 1.97 (tho 2 is close enough). Generally with Cara/Crystal malts colour is a pretty good indication of flavour.
No malt can be directly substituted for another, they aren't identical even if they are close to the same colour. and some times you will need to mix a couple for one malt. Classic example being Fullers ESB, its made with 2 malts, Halcyon Pale Ale and a medium-medium dark Crystal malt that they have made to specification - we cant buy that malt so most home brew recipes end up being 3 malts to get closer to the target.
Here are some possible substitutes (doubtless there are many more), remember the numbers are typical middle of a range and you need to look at each delivery to nail the exact colour and do a bit of testing to get the flavour you are looking for.
So for 20 you are looking for a malt around 40 EBC...
20 oL > BB Caramalt 54 EBC, Weyermann CaraBelg 35 EBC, Weyermann CarraRed 45 EBC, TF Light/Pale Caramalt 35 EBC
40 oL > Weyermann Caraamber® 70 EBC, Caramunich® Type I 90 EBC, Bairds Dark Caramalt 75 EBC
80 oL > BB Medium Crystal 135 EBC, W - Caramunich® Type 3 150 EBC, TF Medium Crystal 150 EBC,
120oL > BB Dark Crystal 250 EBC, TF Dark Crystal 240 EBC, W - Caraaroma® 350 EBC, (at a pinch, I love this malt but it gets very dark very quickly)
Hope that helps
Mark