A T trim fits the S trim bracket, but I seriously doubt you'll see 15# on a 408. 2 reasons first the blower isnt that much bigger or efficient although it is an improvement. Secondly, there is no way you'll be able to get a belt/pulley/tensioner setup that will spin it close to fast enough.
I never had the T trim on my truck, but I do know that you'll run into problems with the aftercooler running higher boost on a T trim.
Im considering having my 6.0 made into a 370 due to the downtime Im facing currently as well. I think the smaller stroke is preferable when you are wanting big boost, of course I havent seen anyone with 408 having problems with the longer stroke.
Anyone know what size pistons and rods?? Im thinking I should keep my eyes open for a deal. Any specifics on the pistons I should look for? 4.030" bore and a 3.622 stroke ??? What length rods?? What do I look for??

 

hmm 370 or 408 , the 370 would be cheaper since i could use the stock crank, i may stick with the strim for now because the carb legal thing. as for the aftercooling i have a little bit covered i have this for a heat exchanger,



and i could always add a bigger coolant reservoir.the t-trim will be probably be the last step, i just need to get a 4l65e to handle this .

 

that is the trick, too bad you cant get an 80e

 

Give Chuck at FLT a call.

 

i wonder if the 6.2l block would be a good choice for this?