Yes, all Chevrolet and GMC trucks (and cars for that matter)from an inline six to a 454 have the same bell housing bolt pattern.
454's and 400 small blocks have a different flexplate. (external counter weights.)
You can (we have) switch counterweights from a 427 non counterweight to a counterweighted 454 flex plate.
Drill one out and weld the weight on in the correct place. No big deal.
If your interested-
I have a good running 350 and TH350 transmission with the flex plate and converter. It is out of a 1974 Chev. Malibu w/around 80K miles.
I pulled it out of my sons car when we got rid of the car itself.
If it doesn't rain again tomorrow I can try to put pictures up.
Where are you located?
I am in the Mpls./St. Paul, MN. area.
Have a '91 Burb to haul with.
Just looked you up on mapquest, that wouldn't be a bad trip!
arequickfab@hotmail.com
Just my .02
CCDually