340 Intake Manifold

Sounds like it will need to be drilled out and Heli-coiled. The LD4B is a good manifold but its actually a 318 intake and has small ports. Not really a big deal if your not looking for every once of power. It would be worse in my opinion to run a 360 port intake on 318 heads and its done all the time.

If you decide to replace the intake The RPM and RPM AirGap are hard to beat but the old LD340 ( That the 340/360 Version of your LD4B) and even the stock 340 intake are good choices.