7.3 PSD Van help

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Hey I realize this may seem a little out of place on a primarily big truck forum. Same engine though so here goes. I recently purchased a 98 1 ton Club Wagon w/ a 7.3 less than 80k. Im doing some mods and building a Veggie fuel system. So far so good. Suspension lift is done, Stainless steel custom fuel tank most of the plumbing etc. Now Im getting into the engine bay and there is little to no room for mods.

I need some suggestions for a different air filter set up, Im not really sure if I have any decent options on the van. I also have one total newbie ?
Why are all performance products sold up to 97 and 99-03. According to threads and info gathered on this site I have determined that this is an earlier engine. Was 98 an either or year? Im also interested in putting a propane injection kit on this but again no room. Ive got to squeeze in a little plumbing, a coolant filter and what ever else I can dream up and finance. Any help would be great even van specific maintenance. Everything is close quarters under the hood.

Thanks