Looks like tar, I would look up a new one(or nos if you can find a pic) and see what it looks like.

 

Haven't looked for NOS but all the new ones come with no cap or tar.

 

Just my 2 cents .... I love that it fired right up and ran good. Naturally it is not going to be dependable as things that are old are going to fail, spark plug wires, fuel & brake lines. Hydraulic brake parts etc.... It is nice to know you have good bones to build around.

Just looking at the rust on the fuel lines coming from the unit .... knowing you have to drop the tank to replace it .... I would not even consider putting that unit it back into service.
I would clean the tank inside and out as good as I could while it was out, I would paint the exterior of it to help prevent future rust. Put it back together with new pump, sending unit, lines.

I always suggest the best quality fuel pump you can afford, just such a hassle to replace in most cases. .... Wife father replaced fuel pump in moms car with a $16 unit from Rockauto and then gave the car to the wife when mom passed .... the pump lasted about 12K miles and I had to replace it a 2nd time because I helped him the first time
Just saying, no fun doing the same job twice.

Long story short, toss that thing in the trash and lets see what the new replacement looks like, if anything to worry about on it.
And I'm a penny pinching old fool retired on disability with a truck project .... I have to watch every penny .... I would not mess with that pump.