Go with a factory dampener and good to go vs wasting money on any brand of fluid dampeners on the market unless your einging it 5-7K rpm's most the time. These FE's all have a heavy cranks not known to have cracking issues even being cast vs forged cranks. One exception the cast 428's which should be checked for possible cracks before spending money polishing or grinding journals. Even then it's not that common of an issue with 428 cracked cranks considering 10 out of 11 of them I have were crack free. The cracked 428 came out of a Mustang drag car with 4 spd hammered down the 1/4 on weekends for several years at 6,800 revs.
Back to dampeners, they were pressed on not vulcanized and over time could of slipped throwing the timing marks off. A must if the rubber is still sound is to check that zero -0- marking matches the piston at true TDC when the heads were off. If not at zero make a note and allow correcting when timing the engine. Who times a FE anyway to factory timing specs unless "good enough" is your thing? Mechanical and vacuum advance tuning as there is a lot to be gained, it's all in the details understanding these FE's. One good idea is to scribe a line across the hub and dampener ring allowing checking if the ring had slipped. Dampener along with crank, rods and pistons plus flywheel or flexplate all zero balanced makes for easy parts swapping not creating vibration issues.
Backing up 95 to 98% FE's were internally balanced so not an issue finding a replacement dampener, pony up not like your replacing it every year. Beware of the 428 dampeners (good luck finding $$$ one) they are externally balanced as well the flex plate or flywheel in two amounts out of balance. You don't want to make a shaker more than the factory run of FE engines which where not been dead nuts perfectly balanced.
I never had an issue being out of balance or requiring balancing after adding forged pistons, 13/32" LR 427 rods (polished & shot peened) on a standard 428 crank which was converted to internally balanced vs externally only at the flywheel end dampener end factory zero balanced. The 410 FE build a smooth engine 35 years and counting running clean at 273K miles. Has 427 LR heads w/stainless valves, hard exhaust seat inserts, roller tip rockers, built to run on unleaded rubbish back in 85......~~=o&o>.......
