What is an l29 motor anyway?
Edit. Nevermind. I just looked it up. It's the 310hp with cast internals.
Mine is not an L29. It's a 385hp mag

Can I email pics to someone so they can post them?

This is the one thing that is a +/- with this site. Thing the site would make more money if they required folks to pay to sale anything. Either way, you have to sign up and pay a fee to be able to up load. Otherwise go to photobucket or google pics and link to here.

Agree, the 454 MPI is a 454 with 502 heads

454 magnum and 502 magnum use the same gm heads.

Yep . The l29 is the one with flat tops . The 7.4 mag uses 9 or 10cc domed pistons to complement the different chambers of the non vortec head. If i remember corectly the dome size was the same on the 502 je pistons , and the extra cubic inches of the 502 block under the 099 heads gave the 502s an extra .25 compression ratio.
But it is still early , and i have not finished my grande burrito yet.

Only time i have seen a forged crank and 7/16 rods with flat tops in a 454 boat motor is when a blower was put in the loop . Or a head swap ,or both

https://goo.gl/images/niMiDK
They look like this exactly

So what makes you sure they are forged? Do you have a part number for them? Because generally that piston is not forged unless it is an aftermarket piston.

Doesnt look like a mag piston to me. Looks like the piston that came in the 7.4 engines, with cast crank, etc

correct,i just took the heasd off of a 1990 330 and that is exactly what i see.my guess is the engine in question is not a magnum.a merc 330 has a cast crank and cast flat top piston.