Please post some links or pics of your chipper. Three things come to mind.

1. The starter is binding and need spaces/washers but why? Add them if they will work.
2. The tank must be plastic or why can the metal not be repaired (brazing or soldering)?
3. A leak proof can should be possible if needed using the proper seals and fittings.

Its a BearCat with a plastic tank

Plenty of dead engines end up in the trash or at curbside. Scrounge one and use the tank. I would suspect that the starter housing is slightly bent and you might be able to bend it back in shape with your hands.

Your problem is the starter clutch on the end of the flywheel. It needs to be replaced. It has a series of ball bearings which allow it to spin freely in one direction and lock up in the other. Order new clutch 399671 about $20 to $25 ($15 to $20 on Ebay).

As for the tank, I think you're stuck. Even on Ebay, new ones go for $75 to $100, and used ones are north of $50 for p/n 691993. Someone does have an older steel tank on Ebay currently at $20. Should work for your application. See the URL below.

Here is a link that might be useful: Ebay Briggs tank for sale

Starter clutch definitely needs to be replaced. Once I got it off and opened it up, all the bearings and interior was rusted and pitted. Thank you for the help. Now I just need to order it.

For the gas tank, I used a thick clean plastic vinegar bottle and installed a rubber valve bushing and fuel shut-off valve into the bottom. For a new tank it would have cost $80+, my cost was $10.13. It would have been less but I wanted a shutoff valve instead of just a thru-valve. For what I need, this will work as I can hang it up out of the way on the handle, while the machine is running. Its not pretty but it works!

Starter clutch definitely needs to be replaced. Once I got it off and opened it up, all the bearings and interior was rusted and pitted. Thank you for the help. Now I just need to order it.

For the gas tank, I used a thick clean plastic vinegar bottle and installed a rubber valve bushing and fuel shut-off valve into the bottom. For a new tank it would have cost $80+, my cost was $10.13. It would have been less but I wanted a shutoff valve instead of just a thru-valve. For what I need, this will work as I can hang it up out of the way on the handle, while the machine is running. Its not pretty but it works!