Run what you can get your hands on. I have tinkered with LT1's for 10 years, and LS motors for 7.

Roadmaster accessories are the same as Caprices and Impala's. What car is your LT1 out of? If it's out of an F-body,and you plan to use a Roadmaster/Caprice/Impala (aka B-body) accessory drive, make sure you get both the crank hub and balancer from the B-car too. The F-car and Corvette hub and balancer don't line up with the B-car belt track.

Motor mounts. Do you plan to run AC? If not, this gets easy. Use SBC motor mounts left and right side. You'll need to run and AC eliminator pulley, but they are $40 or so. If you run an AC compressor, you need the LT1 motor mounts. The right side is unique and puts the motor mount ~1" further rearward. You might also have to dimple the crossmember to clear the rear of the AC. If you are lucky, try to find a set of Corvette accessories, everything goes on teh drivers side of the motor, and you use regular SBC motor mounts. While it's easier to do if you plan to run AC, the Corvette specific PS pump, alternator and AC comp are significantly more expensive if you have to buy it.

If you have any Q's feel free to ask. I've done several LT1 and LSX swaps. Either one will be big power upgrades for your Blazer.