H2 is 190" long with 122.8" wheelbase.
K5 is 185" long with 106.5" wheelbase. Will you stretch the body or section the frame shorter? A pickup truck is a closer match with SWB ~117", but H2 has the rear axle closer to the rear than a pickup bed.
An easier approach would probably be fitting the H2 drivetrain into a K5. You'd have to decide between retrofitting torsion bar IFS and linked airbags or staying solid axle/leafs. When looking at retrofitting H2 suspension, there may be other options that don't cost any more and end up more desirable, like the ORD 4-link/coilover kits.
If we're talking blank checks, there are custom K5 chassis available now that pretty much duplicates and/or improves late model GM stuff, but fitted to a Blazer. Google away, but here's some examples.
https://roadstershop.com/chassis-and-suspension/vehicles/1973-91-blazer-4x4/
https://patriotchassis.com/custom-full-chassis/