Conversions & Hybrids - What to do with the 5.3/4l60?

Here's what is going on. I have a 96 gmc ext. cab. 2wd that the trans went out. Well couldn't find a trans and the rebuild was kind of pricey. Found and purchased a 03 5.3/auto which I was planning to put in the gmc.
Now i've found a guy with a 4l60 trans that will work with my truck for fairly cheap.
On the other hand I've been driving my 1965 4 dr nova which is all original with I-6 three speed on column.

So...

A) Keep to the plan and put the 03 engine/trans in 96 since it will be the daily driver.

or

B) Put the trans in truck and wait for the engine to go (engine has 190,??? miles, but still runs good and gets 18-20 mpg)
and then I could put the 03 engine/trans in nova

C) put the 03 engine/trans in pickup and wait a bit and find a ls1, etc to put in nova.

Just looking for opinions.
I'm leaning toward option C

Option c, that way you can learn the do and donts on the truck that doesnt matter much and do a real nice job on the Nova.