The trans will bolt right up to the block.
What you are running into is Chevrolet used two different bolt patterns on the torque converters, the Th-350 converters typically have a smaller bolt pattern of the two, while the 454 would likely have had a TH-400 with the larger pattern. Only about 3/4" difference in the bolt pattern diameter, But it's enough to make it not fit.
No big worry though, you can get new flexplates that have both size converter bolt patterns on them, most replacement flexplates also have both patterns on them now days.
You need: Big Block Chevy 454, External balance, 2 -piece rear main seal style with dual bolt patterns(6 pads)...here is one example, search that number if you want to find a better price...
CHEVROLET Pioneer Automotive FRA-111 Pioneer Flexplates | Summit Racing
Another:
CHEVROLET Summit Racing SUM-G102STK Summit Racing® Flexplates | Summit Racing
What you are running into is Chevrolet used two different bolt patterns on the torque converters, the Th-350 converters typically have a smaller bolt pattern of the two, while the 454 would likely have had a TH-400 with the larger pattern. Only about 3/4" difference in the bolt pattern diameter, But it's enough to make it not fit.
No big worry though, you can get new flexplates that have both size converter bolt patterns on them, most replacement flexplates also have both patterns on them now days.
You need: Big Block Chevy 454, External balance, 2 -piece rear main seal style with dual bolt patterns(6 pads)...here is one example, search that number if you want to find a better price...
CHEVROLET Pioneer Automotive FRA-111 Pioneer Flexplates | Summit Racing
Another:
CHEVROLET Summit Racing SUM-G102STK Summit Racing® Flexplates | Summit Racing
