Semi gloss is WAY better than flat. The flat paint/primer, will absorb water, will hold dirt... real tough to clean, and the washing and scrubbing to get the dirt out will rub the finish off. Ive been there on 2 trucks, and I did this to get the same look, but not be so crappy. The black rattle primers will fade too, within a year, it'll be somewhere between black and gray.
So here's what i used;
Here's how my truck came out;
And here's how I did it;
http://67-72chevytrucks.com/vboard/s...d.php?t=214871
Kinda long thread in the link, however, there's plenty of awsome advice in there.
There is something to be said for holding out untill you can afford real paint, however, it sucks cruising around in something that looks like a gypsy wagon. Esp in the high school parking lot. Multiple colors is THE WORST thing to have when your buddys are razzin you about havin an old truck instead of a 3 year old Honda. Make it look cool, a couple old school stickers go a long way, as do the pin stripes. You can put scallops, or the pin strip flames on and not spend much money.
Just have fun with it.