A poster over at Ford Muscle said it was 94 also. I could have sworn there were earlier HO versions the were roller though.
I prefer to avoid the reduced base circle cam method. I'm putting together a very mild 351 to replace the 302 in my 1/2 ton.
The introduction date was very late 1993. The conclusive feature is the casting number of F4TE on the block. Unfortunately it's a little hard to read as it's on the underside of the block, just above the starter motor.
Lightning pickups used this block but had a flat tappet cam installed.
any 94 up 351w block found in vans and trucks are roller compatible. You can also take any 69-93 block and use link bar lifters which at least the comp ones will out perform stock style roller lifters in all aspects, OR use a small base circle cam and stock stuff but not the greatest choice on an all out performance engine to go a roller 351w. If your looking to go radical any 351w can be fitted with a solid roller cam.