Are there any places online to get special size of mufflers, or would I be better off going to a local muffler shop I'm wondering?

Need to be 12" overall length, with 8" body length.
6" body diameter-maximum.
3" center inlet.
2.5" to 3" offset outlet.

There is a brand/style called Low-Back that might fit your parameters. The length is the hard part. I would start at summitracing.com and plug in your values.

click here... https://www.summitracing.com/search/part-ty...Order=Ascending

Good selection at the edelbrock site too.

Your small size almost sounds like an old school round glass-pack "muffler" from the 60's-70's (BTW - "muffler" is in quotes, because they didn't .... much ;-) - which would probably be from a local Hot Rod shop, if the ones above don't have anything.

Back in `69-71 I put a little glaspak about your size on my 68 Opel Kadett, which IIRC was called the "Firecracker" which gave a good sound to it's tiny 1.1L I-4 for half the price of a new stock one (HS & college kids are cheap), but I don't know if they're still made.

Try a PM to Curt/cabinetmaker to see what he used & where he got it in Tulsa.

Most of the other aftermarket 914 exhaust systems back in the day & now will bust your limits in one or more of those dimensions.

Good Luck!
Tom
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Not sure why he wants two of them, as before it had one. Need something more quiet this time around. Tired of wearing the ear plugs.

I don't know, but if I have trouble finding the correct muffler, I might have to make my own??

https://www.youtube.com/watch?v=JmFPrDyScHI