I would never ever go back to a carb motor. But in your case and the money thats already in the 406 you have then I would keep it.
fyi the iron ls1 would cost 2,500 max new just some info for ya.
2006 Silverado aka (Bad Bitch)
K&N CAI, Diablo Predator, muffler delete, and a vette servo. 14.7x @ 93 mph (sold)
1998 SS Camaro aka (Silver Bullet)
LS6 intake, ported TB, LTs, ORY, cut out, and a pantie dropping tune by Nelson. 12.6 @ 110 mph 327 hp 347 tq
2011 ecsb silverado aka (silver sleeper)
forged 6.2 and a small snail