You need to find a shop that has a swag / swager machine, an hydraulic expander. Find a local cheap Chain Muffler Shop? Like Midas, Muffler Man etc. If you have anything like that around you. Most shop guys would help you out for a coffee or lunch.
At least I have done this local.
With your clean ride! I am sure you want to do it nice with precision!
Livin in "CheektaVegas, NY
Still have a Kaw! 76 KZ900 Pro-Street.
Went thru 25 of these in 40 yrs.
And The Old Girl, Harley 75 FLH Electra Glide,
Old faithful! Points ign. Bendix Orig. carb.
You can also pick up an exhaust expander tool (AKA a pipe stretcher) for not a lot of money - probably a bit less than another set of stacks would cost.
Or if you don't want to buy one (perfectly understandable) you might be able to rent one from a DIY hire shop. I'm not sure what options you have there; auto parts stores in the US often have tools to lend/rent.
1979 KZ400 Gifted to a couple of nephews
1967 Yamaha YCS1 Bonanza
1981 Yamaha XT250H
1981 KZ440 LTD project bike
2013 Yamaha FZ6R