There is some free spots to the multiclass league in LFS, called LFS LeMans League.
The classes are GT1 = original GTR cars and GT2 = regulated GTR cars according to the MoE classification.

Next race is this coming Wednesday 27th at 7pm UTC

Track: Blackwood GP.
Race length around 1,5 hour.

We have been driving since September 2007 in this Season 2 league but you are welcome if you want multiclass endurance racing for the fun of it.

More info: http://www.lfsforum.net/forumdisplay.php?f=96