Anyone have a clever way to compress the valve springs while the engine/heads are still in the truck? I'd have compressed air in the cylinder to keep the valves up.

 

Do you mean besides using a valve spring compressor tool? I have improvised in the past, but the purpose-built tools are fine. You can borrow them from auto parts stores.

Are you trying to replace valve stem seals?

 

Yep, replacing the valve stem seals.
Several hours after I made the initial post, had a thought. Back in the late 80's - early 2000's I played with '86-'87 turbo Buicks. Since the Buick 215 is the grandfather of the LC2 (3.8, 231 V6) maybe the valve spring compressor I bought over 30 years ago would work.
It does. Just had to shave a little off the sides to pass the keepers and voilà, Bob's your uncle! It is just a standard 3.8 rocker used from '70 to '87, notched on the valve end and a tube welded to the pushrod side for a lever.


'87 Turbo Buick Head. 3.8 V6.

Rover V8 rocker shaft.

3.8 V6 rocker on Rover V8 rocker shaft.

 

Now that is clever! Thanks for the photos.