The biggest problem with the 2-liter six is that they are too small,(opinion) when for the same space a 2.7 would be so nice. Parts have been no problem for my project car, but I've had to wait a while on some of them. There is a peculiar variation in timing belts on some: some have "square toothed" belts, some are like they are now, with rounded tooth belts. The square tooth ones are known to last only 30-40K mi. You must know what you have before ordering! If you don't know when the belt was last changed, change it NOW.(Also the idler)
If the engine is in good basic condition, you could expect it to last to 200K easily with regular oil changes and timing belts on schedule.. Mine has 166K and runs like a new one. When it gets tired, swap in a 2.7. Tom '79 320/6, etc