Difference between solid roller and flat tappet

Well, dropped my stuff off.
Pistons poke out enough gonna need a Cometic gasket. Either a 45 Or 51. Looks like they are close to 10 out.
I had the heads worked a little by a local guy several years back to pick the car up enough to run 11.50 index in dead of summer heat.
We then sent them to the local NAPA to have them milled enough to with a thin gasket(028) raise the compression up.
The pistons were 30 down in the old 360.
Well, first thing Jack noticed with my heads was the intake valves were super shrouded. He said there was 20 horse just fixing that. Said the chambers were the real key with Eddie heads.
I asked, after he looked at them what he guesstimated they might flow. He said 255-260, just taking a quick look.Less than i had suspected.
Anyhow, going from 360 to 418, 10 to 12.5 ish compression, the head work he is going to do( nothing super involved, said maybe 275-280 max) Fresh, quality valve job, nice single plane, vice the old airgap, an 80 horse gain wouldnt be out of the equation.
I ran a “ new” cam Howards now offers by him, its 268/274, 630 ish, 640 ish with my 1.5 rockers. Current is 260/264 565/565. Both are on a 106... that big one would sound ultra choppy.... i like choppy..lol
Before doing that, we will flow the heads and see if as he put it... “if they are still pulling at 600“. Otherwise just put the old cam back in and call it good( more than likely what I will do for now) we will see... might need different springs, etc to do that