What about changing the oil and filter altogether? go buy some SAE30w oil w/o detergent for 1.15 just about any good cheap oil source... Dollar General for me lol. That and a generic filter for $3 and you have a 4.5qt motor, so that'* a $9 oil change. Can't get any better than that.
Try also pulling the valve covers to see if the valvetrain is alright. The front one comes off in a jiffy, so if that one looks good, the rear probably will too. If it'* all sludged up or the metal looks all warped and degraded [bad oil] then uhh your f'd. Or check if the rockers are loose, if they aren't horribly loose and the bolts aren't finger tight it isn't going to be making any noise or at least any loud noise.
If you do have an oil pressure gauge [probably don't tho eh?], if that takes a long time to rise up, that'* a sign of clogged crap oil, and if it'* crap psi to begin with, then she'* done anyways. A quick check with just a dummy light, is timing how long it takes for the light to go off after a dry filter prime. Mine [a 40psi solid motor], takes about a full second with a primed filter for the pressure to start building.
Bad harmonic balancer is an easy check by grabbing the alt fins and trying to rotate the pulley to turn the belt. If it'* all loose and rotates the belt a bit and has an audible hit to it when it grabs, that'* a bad one. If it'* tight so that all your strength can't move it just a bit and it'* more just alt pulley grabbing the belt, she good.
EDIT: now that I've seen the video, man that sure does sound like the HB being ****. Test that belt thing out, and see what happens... you'll know. If not, change the oil with some straight 30w, and maybe a qt of lucas if you want to drive the car. I saw all the gauges rise up real quick, and i saw two, so one had to be volts and oil so i'm gonna assume that'* good, but may be thinned oil, mixed with caustic bad gas.
'89 SSE - GX3 -190k, 155k on body - Back for another ride.