Help with upgrades on 87 GN

[BUICKGREG65]

Hello everyone.
I've got an 87 GN which appears completely stock save for a test pipe in place of the cat on the exhaust.
It has 145K miles. It apparently sat for a few years in a barn. Paint is rough, but mainly rust free.
It has a broken trans mount. Seems to run ok. No knocks, ticks, smoke.
The LED tach and boost guage are crap. Shows boost at idle. I havent nailed it, but it does seem to overboost even at 3/4 throttle (only did that once). I am on a very tight budget and want to do a good tune up (plugs, wires, fluids) and the spring cleaning (where is that located at again? It's been almost 10 years since I got rid of my last turbo buick.)
I'm also looking for used parts since I'm on a budget. First thing I need to get is a good boost guage to verify what I think is overboosting.
I always loved these cars, and the buick guys have always been great. I love to be different, always have, so boosted buicks where just a natural progression from the 400 and 455 Pontiac TA's I was into years ago. Thanks in advance for any help.
Greg

 

[Guess]

http://www.gnttype.org/maint/basics.html

My stock timing chain went out at 140k, or about 500 miles after I bought it.

 

[BUICKGREG65]

OH, found the spring cleaning list.

 

[blackdeathtrap]

check for leaks pre turbo as i said in other treads would seem like over boost could be knock cause by faulty signals because of the leaks get a scan master get a boost gauge post the readings and go from there