Repair-It

A converter upgrade is not out of the question. Gears might be too much for the Fleetwood. That's more a Caprice/Impala thing.

Although I do like the 1500-1700 RPM cruise on the highway...

If 90% duty cycle is acceptable (it's a bit on the high side), the stock injectors will support about 345hp. The problem with 90% is it probably isn't going to work at high RPM. At high RPM where you need more fuel, you run out of time for the injection event. So duty cycle increases with RPM even if pulse width is static. Which is why 80% is a good conservative estimate for injector sizing. In which case you're looking at a max of about 305hp. I think the fuel pump can also support that.

Stock injectors are 24 lb/hr @ 43.5 psi. Standard upgrades are Ford racing SVO injectors (24 @ 39 psi or 30 @ 39 psi).

You can also play the injectors by ear, if you think it's going to be close. Data logging will clearly show duty cycle.

300 hp will liven that tank up a bit.

You don't need a cam to add 40hp. But you need all the bolt-ons...

Here's what something like a 238/242 sounds like on an LS6.

https://www.youtube.com/watch?v=vjtgXTgxRCo