WEC's link to lighting FAQs is a good one, study it thoroughly.
IMHO, you'd be far better off simply replacing your current DOT-code lamps with E-code models. Probably a lot less expensive than the modifications you'd have to make to the front end to get the projector lamps to fit, too. A full set of four (two low/hi, two hi) will set you back about $250 or so, but, seriously, what price safety.
E-code Cibie lamps are available also from www.cibieusa.com
FWIW & HTH. . .