Help with 340 compression + cam change

I think your trap-speed is telling you something;
98 mph is a W/P ratio of 13.0, which at 3200 plus driver is say; 3380/13=260hp
but even if you meant 3200 race weight; then 3200/13=246hp
My factory stock 1970 340 Swinger @3310 me in it pulled that 98mph trapspeed...... with 3.55s, (255hp)
So My opinion does not agree with others here.

If it was mine, I'd be tearing it apart, looking for the problem in those low-pressure holes. And that 284/218 cam would not be going back in; not ever.
If you are trapping at 98@~5300rpm you need a cam that matches that, and [email protected] ain't it. That 218*, coupled with 160psi is a good street pairing, but, IMO, your 4.10s/hi-stall, are giving you the impression of good performance, by multiplying the torque you have, to a higher feel-good number. This is my opinion. Obviously this combo is not optimized for the track. The 284*, with it's late-closing intake, is what is reducing the cylinder pressure so you can run pumpgas. The proper,IMO, advertised duration for a [email protected] would be ~264 [email protected]. But, your cylinder pressure would probably rise into the detonation zone. So the 284/218 cam is doing what it is intended to do, but certainly doesn't or shouldn't need 4.10s nor a hi-stall.

At 160 psi with iron open-chamber heads,in all 8 holes; you can't go much larger than the 284 cam, but you can certainly increase the .050 numbers from 218* to something faster, like up to ~240*. That would be 3 cam sizes and ~600rpm higher power peak; so now ~5600. With the new-found power, the trapspeed will rise to maybe 104@5600 so now your components are better matched, and your ET is guaranteed to fall; maybe to as low as to 13.4. Which is still off the mark for that combo.

I agree with the XE275HL. At 275/287/110+4, 231/[email protected], .525/.525 lift this is a great street cam, especially for factory X/J heads.About as big as I would ever go. Oh wait, that is as big as I ended up at on the third try,lol.
You will pick up both low-rpm torque, and at peak,2 cam sizes worth of power over the 218, and it will run pretty good with the 4.10s. But the 275HL is gonna require a higher octane gas, cuz the cylinder pressure is gonna rise. Maybe to 165 which is generally considered border line too much for open chamber iron heads. You may have to retard the cam up to 4 degrees to bleed the pressure. This is OK cuz on the track it will better match your trap speed, and with 4.10s you won't notice the low-rpm torque loss, because you are already used to 160psi, and the 4.10s/hi-stall..
But before I would do anything,I would, as I say, chase after the why of those low-pressure holes