Can someone explain to me where those chains on a tranny jack are supposed to go? Are they a safety feature?

Also - how does one know the ideal position of the bottom support. Once you un-bolt the bell housing from the engine, could the weight alone of the trans cause it to slip off the base instantly?

This is a low profile floor type - pictured here:

http://www.torinjacks.com/ProductDet...x?ProductID=85

 

Use common sense on attachment. every transmission is different.

tilt the lifting plate on the jack or place shims (wood blocks) between the tranny and jack to get the right angle and then use the chains to secure the tranny to the jack. If you don't, THEN it's going to fall instantly off the jack.