Farms, I ran into the same issue on mine several years ago. What I did was used my old flywheel from the 350 on the 454 - I ordered a counter balance plate.
I have used these many times in the past and never had any issues.
If you are not familiar with these, you can find them at many different aftermarket parts warehouses.
They run $20 - $40, depending on the one you need. Usually much more economic than purchasing a flywheel.
An example of one is here at summit
https://www.summitracing.com/parts/ses-3-60-11-026?rrec=true (I am thinking this is the correct plate for your application).
Call them and tell them that you need one to use your 350 flywheel/flexplate on your 454 and they will give you the correct part number.
