how much nitrous?

i have a 89 305 tpi and lookin for a nitrous kit. how much could my stock(flowmaster exhaust & k&n) engine take with out messing stuff up?

How many miles are on this engine?
If this is the original engine and there is alot of miles on it I would do a compression test first.The car will be fine with a 100 hp shot.The engine should take a 150 hp shot but I recomend upgrading the fuel pump to do so.
Dave