Adding Lead Ballast. Tips and tricks?

Blimey, the SF boat in your avatar is MUCH heavier than I would have thought!
Jokes aside, any tips about ballast placement and best way to secure it depends a lot on the specs of the boat involved, imho.

Has the vessel had a stability test? Have you consulted with the naval architect? I would think they would be the first steps to adding ballast.

35' Cabo express with a lot of anchor chain comes to mind!

In my first reply I didn't notice that you were talking of a longitudinal listing.
If it's something that you are considering to cure with 1500lbs of ballast on a boat of that size and weight, it can't be so annoying, and therefore I'd rather live it well alone.
OTOH, if it really is so bad, I wouldn't waste time experimenting with such relatively small ballast, and I'd look for professional advice, as already suggested.
All the best!

larger yachts it's entirely common to trim with fuel. Since there is a cockpit, the aft fuel tank is ALWAYS the last one you drain as that is what counteracts the bouyancy of having a hull with not much weight above it (no super structure). How does the yacht sit when it's full of fuel? You bought a Taiwanese tub that they put a cockpit on an existing shorter hull design at the factory without moving anything, so keep the aft fuel tank full until last. Both for trim, safety, and handling.

I looked at that boat few years ago. There where a long list of issues on board her. Weight distribution is just the start. The boat was still owned by investor who had her built and was very proud on her price. Did you do a thorough sea trial and mechanical inspection? The ponding water at salon door needed to be fixed with new drain. Mechanical systems were rough, zero maintenance done while sitting. Bring her to a good yard and open the checkbook.

One I looked at had pickled oak interior, brought over from Asia and parked. Really was sad to see condition of it after just a few years.