The L31 is a good Vortec head engine. It can make a lot of power with the right cam.
I have a RamJet 350 in my '55 Belair. That engine IS a 4 bolt main L31 with a different cam, 1.6 roller rocker arms and of course the Multiport EFI setup and it's MEFI-4 ECM.
Makes 350HP and 400 ft-lbs of torque.
I have a stock 436HP LS3 in my Corvette and I can tell you that my RamJet has a little better low-end torque than my LS3 has. LS3 beats it on top end though starting at around 4,000 rpm. Redline on the RamJet is 5,500 and the LS3 will pull strong all the way to it's 6,600 redline.
My recommendation to you would be to put the same cam, rockers and valve springs that the RamJet has on your L31. Then go with a Holley Stealth Ram EFI kit for Vortec heads.
You will also want to go with nice set of headers and a 2 1/2" exhaust setup with an H or X pipe.
Also take the time to do a true cold air intake pipe setup.
Yup, you would have a lot of money in it. But it will be a great performer and still retain that great looking Chevy small block engine under the hood.
Very nice Choo Choo you have! Looks brand new, can't believe it has 103k miles! I got mine to handle much better by adding 18" wheels and dropping it 2 inches in the front and 1.5 inches in the rear. Also, when I bought mine last year it already had a rear sway bar installed so I'm sure that helps a bit too.
nice choo choo el camino. wish i could find a nice one like that before i decide to convert my el camino to a choo choo front end. just by adding a rear sway bar it would make it handle alot better than factory.