QX
Welcome to Stovebolt.
OK, you said that in May, before you bought it, it did turn over. So the motor is not stuck, right? Or is it stuck now? I'm confused why you put the additive on everything under the valve cover. Are you using that as a cleaner or penetrating oil to loosen rusted or stuck parts? And what about the additive in the spark plug holes? Have you filled each cylinder full of additive?
Has the truck sat for a long time not being run? Does it have a battery? Is it full of oil?
Somebody that knows carburetors will have to comment on the tag number. That model truck should have a Carter "W" I think.
Do some research on this site
http://chevy.oldcarmanualproject.com/chevyresto/49index.htm
and here
http://chevy.oldcarmanualproject.com/shop/1948_51truck/index.htm

Describe better what's going on and hopefully we can help you.
Good luck.

Professional Novice