Currently running a fbo stock bottom end 5.3, with a built 4l60e. lopes hard, has ls3 stage 2 btr cam, not the wisest choice for a 5.3 but I just want more torque and overall power before I go boosted.
swapping over some stuff engine wise to the lq4

Picked up and lq4 long crank for 125$ w/o heads. Got it home and seen it had newer 4.020 psitons and im assuming newer rods, haven't checked yet as i had to fly back to cali until I'm home in September.
​​​​​out here I can get 6.2 l92 heads for like 125$ from the junkyard and pickup an intake too.

Lq4 build as follows
speed pro 4.020 pistons -.007 dished
newer rods?
L92 heads
Btr dual .660 lift spring kit, with titanium keepers
Btr 7k rpm trunnion rockers
New ls7 lifters and gm tray
7.400 pushrods
Cam idk yet, as I want to gain low end torque
ARP head bolts
​​.40ish ls2 headgasket
ls2 chain
melling high volume pump
Arp rocker, cam, timing cover, oil pan, pump bolts
Arp rod and main bolts with new bearings
6.2 truck intake with dbw throttle body
summit rails with quick disconnect adapter
50lb injectors
vette servo
walboro 450 drop in
25% underdrive balancer
Hinson wires and heat socks
radium plugs
wideband
ac and heater core delete
oil cooler
4in aluminum rad 3 row with 180° thermostat
Long tubes
Cai
electric fan conversion
3200 stall converter
3.42 rear end for now
Hp tuners mpvi2

questions are.
with being 4.020 bore and ls3 being 4.065 I shouldn't have valve shroud issues correct?

according to my calculations, with bore 4.020/ stock deck height at .044in/ headgasket .042in/ piston being -.007cc/ heads being 70cc/ and stock stroke, I should be very close to 9.57:1 correct? With somewhere around .045 ptv
just wandering if switching to flatops would require major fly cutting? Also I would need a ls3 cam grind forsure

Also curious as too if my ls7 style rockers on the 5.3 fit on the l92 heads with it having different angles.

 

questions are.
"with being 4.020 bore and ls3 being 4.065 I shouldn't have valve shroud issues correct?" You won't have any valve shrouding issues as those heads are used on 6.0 trucks too.

according to my calculations, with bore 4.020/ stock deck height at .044in/ headgasket .042in/ piston being -.007cc/ heads being 70cc/ and stock stroke, I should be very close to 9.57:1 correct? With somewhere around .045 ptv Not sure.
just wandering if switching to flatops would require major fly cutting? Also I would need a ls3 cam grind forsure You can use any cam grind you want, just because you are using LS3 heads definitely doesn't mean you need a grind designed for them

Also curious as too if my ls7 style rockers on the 5.3 fit on the l92 heads with it having different angles. Do you mean ls7 lifters not rocker arms? The LS3 style of square port head will need offset rockers on the intake side, and standard straight on the exhaust valve side.

It would help if we know what kind of truck this is planned for . RPM range wanted, etc..

 

I just looked up the Stg 2 LS3 BTR cam specs, me personally - I'd take it out of the 5.3L and reuse it. It won't be as "lumpy" or "soft" down low in a .020" over 6L. And it will be fine when you add boost to it.
Your compression calculations sound about right, a stock LQ4 is advertised at 9.4:1 SCR.

 

It's for an 03 silverado 1500 2wd. Ext cab short bed, gutted for the most part. If i recall right, it was 4421 on the scales with me in it. No rear seat, spare, hitch and carrier, rear bumper, has roll pan, talegate net.

Decided to go with 241 heads that I'm porting. Got them dirt cheap invery good shape. Should put me at around 10.47:1 or so compression.