I would find another muffler shop. I just had my whole exhaust system replaced using an NOS muffler on my 63 F-85 and my man used one pipe from in front of the rear wheel to the muffler. He did several bends matching what the factory did. None of them are close to 90 degrees.
I have used sealer like Eastwood sells with a lot of success about 10 years ago. Now that a lot of gasoline has that [b]Ethanol[b]crap :angry: in it you need to make sure the sealer is resistant to ethanol.
