First timer updating a mod - need help with balance

[The Ideal Gas Lawyer]

I'm trying to update the Jool V parts pack for .22/23 since it seems to be abandoned by Bobcat Industries. It was originally made sometime around .18 iirc, the screeshot gives you some idea how old it is. I know other mods add comically large SRBs and massive 3m tanks/engines but I always like these and thought it would be a fun way to learn. I've never done anything in the way of modding but by looking at config files for stock parts I'm stumbling my way through. I've gotten the parts working by wrapping the "Part {}" brackets around the whole file but now I'm trying to figure out what values to add for the new parameters and how to balance whats already there. There are three main parts I'm trying to figure out the balance for. The SRBs, the first stage engine and the second stage engine.

SRB: oldValue - newValue

entryCost = XXXX - 3000

cost = 800 - 1200

mass = 1.75

breakingForce = 630

breakingTorque = 630

maxTemp = 3900

maxThrust = 1200

heatProduction = 500

atmosphereCurve

key = 0 320 - 275

key = 1 280 - 245

RESOURCE

name = SolidFuel

amount = 3200

Main Engine:

ValueentryCost = XXXX - 40000

cost = 850 - 3850

mass = 20

breakingForce = 630

breakingTorque = 630

maxTemp = 3600

MaxThrust = 7000

heatProduction = 470

atmosphereCurve

Key = 0 390 - 330 (same as mainsail)

Key = 1 300 - 280

Second Stage Engine:

ValueentryCost = XXXX - 30000

cost = 850 - 3300

mass = 8

breakingForce = 630

breakingTorque = 630

maxTemp = 3600

MaxThrust = 2800

heatProduction = 500

atmosphereCurve

Key = 0 390 - 350 (same as Skipper)

Key = 1 300 - 300

I've added all three to the "Very Heavy Rocketry" TT node but I'd like some feedback on the other values I've chosen or have yet to chose. Mostly I'm struggling with the Isp since I know it's OP right now.

[jordanjay29]

Way overpowered. That main engine gives almost 5 times as much thrust as the Mainsail engine. I'd put the ISP for it way down to 175 or so, more if you're going to be realistic. Power doesn't come from thin air, something has to give, and usually it's efficiency.

[The Ideal Gas Lawyer]

Way overpowered. That main engine gives almost 5 times as much thrust as the Mainsail engine. I'd put the ISP for it way down to 175 or so, more if you're going to be realistic. Power doesn't come from thin air, something has to give, and usually it's efficiency.

My understanding is between power, weight and Isp, you get to pick 2. The engine does weigh 20T. The Isp does definitely need to come down though but I'm not sure it needs to go that far

[jordanjay29]

Stock Mainsail is 6 T, 330 ISP, 1500 kN

Main Engine is 20 T, 330 ISP, 7000 kN

It's up to you, but I'd still bring that ISP down significantly.

[The Ideal Gas Lawyer]

Stock Mainsail is 6 T, 330 ISP, 1500 kN

Main Engine is 20 T, 330 ISP, 7000 kN

It's up to you, but I'd still bring that ISP down significantly.

I'm planning on it, I'm just trying to figure out by how much. I do appreciate your input. Any thoughts on the SRB?

[The Ideal Gas Lawyer]

Bumping for more help