will 1/2 ton front end parts will work for a 3/4 ton front end?

Depending on which year, some might. However, I would not recommend putting 1/2 ton parts, especially suspension parts, on a 3500, (it's a 1 ton, by the way), unless it is a very temporary fix and the truck won't see heavy work until stock or better parts are put on.

my suspension is a 3/4 ton by the way. my truck is a 1990 gmc 2500. the only thing is one ton is my cab.