I broke one tranny last year. I got like 40-50 passes on it before stock 1.82 (yes the original inline 6/small block) gearset surrendered. So I'm telling myself that the 1.76 is bulletproof stuff compared to 1.82 and it should take all the beating my 509 deliveres or even more. I think that the low starting line rpms are helping everything to survive.
I was surprised to know that the stock case can take more hp than the stock 1.76 gearset.
But I hope that the stock case & stock 1.76 gearset can take all the horsepower to get the car closer to 8.5's. The next step, 7.9's car, starts really to cost money. 1000+ hp engine, chassis upgrade, aftermarket tranny case & gearset...
With AFR heads I would:
-lose weight on the heavy front end
-Get bigger intake valves (2.19->2.30)
-bigger intake runner
-beefier springs = more rpm (merlins have only 1.550" double 180lbs seat - 500lbs open)
-more flow on intake and exhaust
Besides, the Merlin heads have to be serviced this winter and I'm not willing to spend a lot of money on them. AFR's aren't a must, Dart also has similar 335 or 345 heads which I believe are in the same level than the AFR.