Are the blocks the same for the 99 as the 93? Do all the accessories bolt in the same?

 

From what I understand the 24valve blocks are a little heavier in the webbing for the mains, but thats the only difference well I guess the head bolt holes and suck are different too, just speculation though.

Jed

 

As far as I know there's no reason you can't put 12 valve pistons in, change the front cover and cam, put on a 12 valve head and all the associated stuff and call it a 12 valve. I'm running a modified 12 valve marine gasket in my 24 valve.

 

If you start with a bare block, you should be OK. a 99 is a 24 valve engine and will have different pistons.
Make sure the 99 block does not have a "53" casting on it. If it does dont buy it, they are proned to cracking.