How do you set timing on a 1994 gmc 454?

for any auto repair, consult your repair manual. if you do not have the required tools, manuals or knowledge to complete the repair then you need to consult a certified mechanic.

any mess-ups that you make while doing your own mechanical work can be catastrophic. engine parts must perform their job up to 100 times per second, and anything that is installed incorrectly can cause bad performance or even system failure, possibly damaging other components and increasing repair costs.