Screws will pull out or fail. I would only through bolt it, If you're not fussy how it looks you could use two pieces of strut to spread out the contact area and straddle the frame with threaded rod. Just drill the bed and make like a trapeeze hanger with strut under the frame, sandwich the block, and pull it to the bed.
Good deals on trucks are gone. I always watch the used Hino's around 16k# gvw, was watching for a Hino 195h. They're all gone. The used ones at 30K are hard to find for 60k. But if you've got 30k to spend, you still might get lucky.
Boch Toyota is the best I know of for pricing and inventory. They had a 2021 white 5.7l Tundra 2wd for 37k list. I was going to post the link but it's gone. 2022 Tundras are 50k+. They had some white 4 cyl 2 wd Tacoma's for 30k list. I was going to post the link to the Tundra but it's gone.
Working out of a pickup, pickup with Reading cap, I've done it and would never recommend it unless you can job by dropping off a gang box at the job and commuting. Choosing between a service body and a van, definitely a van. Service bodies are way too heavy for what you get.
I had a Hino FB with a 12 ft box (van body) and pullout ramp. That was a great setup. If I can get the work for it what I want to do, that's the right size for me. I was getting 16 mpg diesel with an 11k# running weight.