right now i have a saginaw 4 speed from and older nova. i have been offered an M20 for $400. now i'm going to get it nonetheless, but i was looking to learn some more information on it. as of right now i'm building a hopefully a 500hp small block 400 (11.75 compression, solid roller, TFS heads, etc.) i would like to know,

What are the Gears Ratios in the M20s?
What kind of weight will i save by going to the aluminum case?
I heard M20s are good for about 450 lbs of constant driving...true?

Also, my friend told me that the aluminum case will twist and break easier than my saginaw, should i be worried with my combination?

It will be going in a 1960 Chevy Truck, so there is NO factory transmission cross member at the tail shaft. Just the Front plate and the bell housing cross member, then it's hanging all the way to the pinion. should i put in a transmission cross member or will i be ok without it??????

i had run the saginaw with only two bolts holding the top ears to the bell housing and nothing broke.....given it's a cast iron case and only 300-350hp........

please any help is much appreciated

Thanks