If i add Aussie halyard and new shrouds to 1976 h16 is there any problems or other parts I will need this is a real nice old hobie has origional rig I think it is time to replace these we have ben sailing hard last few years it looks good BUT.
Are you saying you still have the original '76 shrouds/forestay? If so, you have gotten exceptional service but I would replace them immediately.
You ask a good question. In recent years the factory supplied shrouds have been shortened to facilitate additional mast rake. (Also, the jib has been recut to accomodate the additional rake.) Before you get new shrouds, you should measure the length of your existing shrouds and match that, especially if you have the original Seaway jib blocks/cleats. Also check the shroud anchor pins and anchor bars (the threaded pin and the bar that fits under the hull lip). I have seen both develop cracks due to salt water corrosion.
To check out the current thinking on mast rake, take a look at the photo from the '04 Worlds for January in the 2005 Hobie calender.
When you use the new (shorter) shrouds you will have to find a soulution to extend your forestay. I used a secound chain plate. between the pig stay and the halyard pulley.
Patrick
I still have all my 1972 standing rigging. I inspect it frequently and have yet to see anything untoward. 
Now watch, I'm gonna get dismasted next time I go out. lol