Hey, it's super cool that you're experimenting with alternate strats to find ways to make levels safer and more consistent!
In this case, it might be worth watching what players do when they miss (or simply don't go for) shell jump - P-speed tends to be maintained, and level end is 3 IGS faster. Frankly, you've got the hardest part of the level (the jumps after the shell) down, so you should be able to shave those 3 IGS off of your IL PB trivially without having to nail shell jump.
Keep at it!
Darn, I was genuinely upset from expecting "New Speedrun Strat in YI4" to be an RTA Reznor Kill.
Anyway, if you're playing on emulator, make sure your key combo presses that aren't used often (such as whatever you use for run, up, and B ) aren't prevented by ghosting, which is purely a hardware thing that exists in most keyboards.
