L460E questions

[Larry S]

I have a 69 c-10 that I'm planning to put a 1996 vortec 5.7/ l460e into. I went to a local trans shop to find out what will need to be done to make the trans work with my factory 69 speedometer and Im planning to make my truck a floor shift. The guy said " theres no way to put the l460e into that truck and use the factory instrument panel." He says the tach in the 1996 silverado (donor truck) tells the l460e when to shift. So he says, I can install the l460e in my truck and I put it in drive and it would never shift out of its lowest gear. Is this correct? He says I need to set the l460e to the side and find a pre electronic l460, or 700r trans. I hate to do that because the one I have has less that 5k miles on it. Is there a way to make it work, or does anybody make any kind of adapter to do what Im trying to do? As always I appreciate you guys!