timing is moving

i have looked and looked cant find an answer that works. when checking my timing with my gun and i have tried others guns. my timing moves, not real noticable with spout out, but when spout is in it will read one thing then another and keep jumping around, newer rebuild on motor, so chain is good, balencer is good, distributor is tight. asked someone else and got some ignorant answers and some rude ones. far from new to mechanics and cars, but very novice with mustangs. i want to have fun with this one but the timing issue worries me, never had this happen on any other car. any thoughts, ideas, opinions, please let me know. im all ears and ready to learn. thanks

matt

89 lx with 306, just in case that matters.

ok whewwwwwwwwww im a newly converted ex chevy guy. i have alot of issues other then the jumping around. like the kid i got the car from i think bought alot of expensive stuff, that is big and expected it all to work together. it doesnt looool. so that is one less thing for more to stress on. i really appreciate the help. im veryy car savy but novice mustang guy so it is appreciated more then you know. thanks take care

matt