I have a 1980 302 stock pistons, early to mid 70's 351 heads 18mm plug holes.
My question is is there a way too check what my max lift would be before i purchase a cam with a larger lift, if so what would that be?
And if any one knows what the lift would be?

 

read the cam specs and know your rocker arm ratio do the math lift x ratio if you still have doughts and can find noone thats done this mod preassemble your engnine with some silly putty in the cylinders to see if the valves and pistons have clearance needed

 

What are you building this engine for in particular? Are you planning on towing a boat or holiday trailer? Everyday driver, and just want a bit more power? All out racing and performance?

Max lift may not be what you want, but rather a matched compression ratio/cam/intake/headers, and aim for a combination that will still run nicely on pump gas.

 

I would like too put something on the lines of a .500 lift and 219 dur @.50 the truck is a little bit of a street runner, it has headers 4bbl and rpm air gap intake, heads have been ported polished and larger valve springs with screw in studs valve guides roller rockers. rear is 3:73's I was tring too avoid going through the silly putty thing but if i have to then that is the way it is

 

You say a bit of a street runner. You might find yourself a lot better off with a mild RV cam...say 260/270, a small 4bbl carb(around 600cfm) and you'll find you have power off the line, and in the mid-range, where it counts. At the same time, the truck will be happy to haul a trailer, as well as get acceptable fuel mileage.

If you over-build it, you'll only find yourself ending up with disappointment in the results. I've seen way to many really "cool" engines that have ended up in street machines...they generally end up falling flat on their face when seconds count.

All that being said, it's your dollar. As previously stated, money is no option. If you want to achieve max lift without tossing a valve through the top of a piston, cc'ing the heads is the ONLY way to go.

Here's a link with some basic back yard based ideas as to how to properly cc a head.

http://www.hydrostream.org/ArticleArchives/CCHeads.htm