1972 chevy c30 weird project

[what66]

Hi, guys, First thing is I want to say sorry for snapping at you guys my depression was really bad that day but I'm back on meds now and doing better.
Ok, I have a weird project in mind I have a c30 1972 chevy I love the cab but not the drive train I can't go over 60mph without guzzling gas and revving the engine.
So I picked up a frame from a 1999 chevy pickup it came for Texas so almost no rust it has a 4l80e tranny and a 5.7 Vortec so I plan to take the 72 cab and front clips and merge it with the 1999 cab floor so I have a 72 with a 1999 drive train. I plan to keep the interior the same in the 72 so it will still look old.
I know this will be a lot of work but I have the parts and no life so why not.
So what do you guys think is this ok or do you think I'm destroying a classic truck?