1998 K1500 pickup - 5.7 Engine to Older Engine

[herrmc]

I have a 1998 4x4 Z71 truck. The engine recently developed a noise.

The noise sounded like a "squeak" of metal under intense pressure (like a bearing siezed up)... almost a thud, but not quite.
The timing of the squeak seemed to be in sync with that of the camshaft (as opposed to that of the crank). The engine "turned hard", and seemed "labored" when it was running... I did observe the rocker arms of all the valves while the engine was running... they were all lifting and dropping... my suspicion is a cam bearing siezed up?

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My experience on the inside of an engine is with the older chevy 350's... I have read a little about the differences... As I understand it this is an L31 (Vortec 5700)...
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I have the engine removed, and intention was to take it and have it rebuilt... but the machine shop that has done my work (and I trust) has gone out of business. I am looking at finding another place.
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My question (in addition to hearing ideas about my squeak)... is in regards to "swapping" out the engine for an older one.
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I have 4 or 5 old engines sitting in my shop (late 70's to mid 80's)... mostly 350 engines... a couple of them are in very good mechanical condition, a couple need rebuilt... one is torn down, all machine work has been done...

As I understand it, I can take the Vortec heads off my original 1998 L31, and put them on one of my existing 350 engines... and do a direct bolt up ???

Can anyone fill me in on potential issues with this before I encounter them?