I've had no problems with the Melling M54DS oil pump.

https://www.amazon.com/Melling-M54DS-Replacement-Oil-Pump/dp/B000C4PO6E

Some like to replace the oil pump driveshaft, tho I've never broke a stock one.

https://www.amazon.com/Melling-IS54A-Oil-Pump-Driveshaft/dp/B000C4LRR4

I repaired/replaced one rope seal, with engine in car.

Went by the instructions in the 1969 Pontiac service manual. Made a tool to drive the ends of the rope up into the groove, as per instructions. Then you cut short pieces off one of the supplied pieces of rope, and packed them into the ends of the groove as much as possible, then cut 'em off even with the block.

Then install the other piece of rope into the groove in the cap, and trim off ends, in the usual manner.

The Best Gasket brand is now considered the best rope seal on the market.

http://www.bestgasket.com/pop_up_picture.asp?PartNumber=6380S

https://butlerperformance.com/i-24452895-best-gasket-braided-teflon-graphite-rope-seal-for-326-400-bga-6380x.html?ref=category:1234758

https://www.ebay.com/itm/Pontiac-40...Main-Bearing-Seal-Set-BEST-/171134712932