Buy a new needle valve for it, a rebuild kit, new hoses, a new Dwyers (since they suck air in with all the little stress cracks) and give it a shot.
Cat thinks that 4 bolt version was worth gold. When I was at Cat last Feb we were working on mine and I told them I wanted a new 4 bolt style. They gave me the price..and it was more than a whole new 435. They looked into the pricing for 3 days thinking it was a typo...but couldn't come up with anything.
Chad