The 4.1 is a nice upgrade a member is offering to sell that will basically look stock. Here is the issue, your car WILL NOT be numbers matching making a 3.8/TH200C pointless, it won't be original. If you told someone you put another 3.8 in on purpose, they will ask why would you want that. A 4.1 with dual exhaust will look original except to experts and give 25 hp over a stock single exhaust 3.8 and get the SAME mileage, maybe more if you stay out of the secondaries. I do get the TH200C over a TH250. A better first gear, less parasitic drag and a lock up torque converter. Of course a TH2004R has all that plus a .67 overdrive, allowing a gear swap to a 3.42 gear, with stock tires at 60 mph, 1850 rpm. I seriously considered making my 1970 Cutlass S look stock under the hood but realized it won't be and I even had the correct #6 heads for 1970 on the 350. It really wouldn't add value and with work it could be a $10,000 car, your LeMans will never be especially with a V6. I got 21 mpg out of the Olds 260 someone put in the 70S. With an Olds 350 making twice the power, it got 19 mpg, same 2.78 gears. Carb leaned out with a 2004R trans on the 350 vs s regular TH350. I probably could have eeked out one more mpg. The whole drivetrain package makes a difference for performance and mpg. Someone told me to light it up, I could for a 1/4 block. I am putting back on headers and duals back on the Olds 260 to see if I can get 30 mpg imperial highway with my 88 Cutlass, 26 mpg so far. I had the headers and 2.5" compact X pipe dual exhaust on the 260 was already on my 88 when I had a 350 in it, it helped a lot everywhere for power. The little 1 7/8" dual exhaust on it now, it really kills the top end, struggles at the 4000 rpm shift points, so the headers and 2.5" system is going back on. Plus I have never heard better sounding exhaust, the same exhaust on the 70, it doesn't sound near as good. Good luck.
