My 2 cents: get a later model Windsor block that is compatible with roller cams. From what I understand, the casting number to look for is F4TE. Past that, I don't know if one year is better than another.....?
Here is what one contributor (jwtaylor) had to say at ford-trucks.com:
"The lifter bores in the roller block are taller as opposed to the shorter ones in the non roller.
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Roller block F4TE. If it already has a roller cam then any old roller cam of your choice would work. The easiest way by far. Or aquire a roller block F4TE that has a flat tappet cam installed. YOu can take the spider retainer, H-bars and lifters out of a 5.0 HO and either use the 5.0 HO cam or install a grind of your choice in your 351. ONe way to tell the difference might be the gear on the distributor as roller require brass and non roller use steel gears. Another option, take the intake off and look for a spider retainer. Pretty easy.
Non roller block. You can drill and tap holes to accept the 5.0 spider retainer, H-bars and rollers lifters from a 5.0, but you will need to use a reduced base circle cam. Another easy option for a non roller block is special lifters from crane that do not require machining of any kind you simply drop the lifters in as usual. They have bars connecting them so there is no need for a spider retainer. You can also use any of the shelf roller cam. All the ford "alphabet" cams etc.. You will need to install a brass gear on your distributor. ......."