i have converted my 1983 320i l-jetronic to LPG, there are two systems i put in the cheaper one where the LPG is released after the air filter, and it goes ok, it's highly recomended to use new spark plugs and new cabels, every start is on gas and after 2000 rpm it changes on LPG and after that you drive on LPG, and it goes ok it usualy spend one litter on 100km more. but with the price of the lpg is really cheaper.
there is another system with a nozle on each cylinder, and far more eficient and it spends just like gas, and with that kind you can make it even more powerfull but it would spend a lot like that.
here is some pic of my car with LPG
if you need any more advice i would be happy to help you ... cause i have experience some with this.
