This is most likely not the cause but worth a shot, I have a L28ET as well and was having real bad sputtering that progressed to the point where it would die. After looking all over I found that the gasket that is under the spring in the pop off valve had shifted enough to make it remain open all the time. This threw off the AFR so much the car ran horribly. Simply put it back in place and the car ran great.
Hey I'm interested in a few things if it has them. The window levers, AC blower, Fuel gauge, and speedometer. If it's got any of those I'll take them! also the little piece to pop the hood (handle).