I wouldn't bother with notching the frame, its worked for some and not for others then theres the issue with wiring and having custom hoses made. I did it just to find out that the lines would run out right into the a-arm mount, but if you still insist on torturing yourself and trying to do it i'll post some pics. Best motor mounts are the cheapest if you ask me, check ebay I paid around 30 I think.
1991 Silverado-L33 5.3L, 212/218 .557 .562 115+4, ASP under drive pulley,180* thermostat, 90mm truck intake w/ LS3 throttle body. Shoenfeld conversion headers and duel Flowmaster exhaust. Performabuilt LVL 1 transmission and 23-2500 stall converter.