I have 2001 GMC 2500HD. 170K on it. Been waiting on it to die so I can build some power into it. pretty much only use the truck to tow (12K) my 24ft enclosed racecar trailer.
Low RPM tq is the goal. 87 octane fuel is a necessity, but I can run 89 if I have to.

currently the truck is 100% stock, less the OEM muffler.

Thoughts are to build a 408 from the motor I have. I see lots of kits out there and have priced the kits vs putting together my own kit, costs are close.
Question #1: Is there a reason to go w/ big money kits ($2k) over some I have seen as low as $1.3K? Right now I'm liking the Lunati kit as the name is reputable and the price is OK. Is there anything out there for less money that would fit the intended use better for less cost? I don't really need a billet crank for what I want to do w/ the truck (stock rev limiter will remain). No power adders (N2O or boost). I saw some Speedmaster stuff that seemed low in price. Worth a look?

Question #2: Any reason to go w/ one rod length over the other? I see 6.125" and 6.1" rod length cranks (and kits). Is there a reason for the difference and what would be best for my use (towing, low RPM). I'm thinking the longer rod would be better for piston rock issues.... right??? My desired comp ratio is 9.5:1 to 10.0:1. I think 9.8:1 is a good target. Would this dictate the rod length in any way? I will be running a small non-stock cam, so I'm thinking I may be able to get away w/ a little more comp ratio. Guidance from those who have towed w/ a 10:1 motor on 87 octane would be nice. I also feel right now, H beam rods are way overkill. It would be nice if I didn't need a $700 set of rods. But if the only option is close to that price.... then why not.

Question #3: Heads...... I don't really want to spend money here. The current goal is to freshen up the stock LQ4 heads. I'm open to swapping to the LS3 stuff (intake as well), but I want to keep low end tq up as much as possible. Running down the highway, the tack sits at about 2.5K. I'm OK w/ that, but it needs more grunt there to stay in OD on even the smallest of hills.

I've done a lot of pricing as of late, and some minor self educating on the current offerings. K1, Compstar, Callies, Scat, so on and so forth. Feel free to name drop anything I missed.


Things I'm not interested in.... supercharger/turbo. Gear change (4WD), higher stall converter.
Idea's I'm open to..... full LS3 conversion (6.2ltr), or swapping the 4L80E over to a 6L80 if possible, or both if it is a worth while swap.

 

Also.....
I'm targeting the 408ci size for durability reasons. I want to get another 100K out of this motor if I can. I don't expect 170K, but 100K would be nice. Any reason to not go bigger??? 421, 427, 454..... ect.....?????

 

LS 408 4" Cast Crank H-Beam Forged Pistons Engine Stroker Rotating Assembly Kit

 

Nice find on that rotating assembly, It would be fine for what you want. No need for forged crank and rods with no power adder and stock rev limiter. Keep your heads, ls3 stuff likes more rpm, not what you need in a tow rig, even with a 408. I personally would stay 220 or less on cam duration, most will say that's too small but I think for you it would be right on. I would also shoot for 9.5:1, I think 10:1 is a little high for 87 and towing. Add headers to the list and you would have a nice tow motor.