Short of forced induction I don’t see bolt ons gaining you enough on a 400 to make much difference. Internal engine work to the head and bottom end could get results but you’d spend far more than the price difference you’d see selling your 400 and buying a larger machine. I’d be looking for an upgrade, as opposed to squeezing what you’ve got.
It’s the cat engine. I have had the same luck finding kits just wrong years.
i Was afraid of having to sell and get a bigger machine.
I read some where if you change the spring out in the clutch but it it didn’t say what spring or from what just not enough info for me to bite.