I don't think the old paint will be a problem. However, since you are going to have to buy new reducer and hardner, an extra 100 or 200 for new paint isn't that much.

You might consider clear coating the laquer to get more UV protection for the paint, otherwise soon you'll be having to polish and wax your truck several times a year to keep it shiny.

'51 Chevy 1/2 ton w/'62 261, HEI, offy, fentons, dual carter/webbers, t-5 & 12 bolt posi