What AT modulator for modified Z & how to adjust it?

[Stanley]

After installing a modified 280 block with modified 280zx head & stage II cam in my 240Z, my AT modulator  promptly blew out and started sucking ATF into the engine. Put a new modulator but it seems to have blown out as well. Maybe the the new engine is making too much vacuum for the flimsy modulators?

Trans is 3N71B, stock 3-speed AT for 240Z, 280Z, and 280ZX, Maxima etc. AFAIK. Looked at Rock Auto, they have same (and some different) ones listed for the various models, from $11 to about $50. Two are listed for 280zx as "fully adjustable", one with a 910" diaphragm for non-turbo, and one with a .840 diaphragm for turbo. The same $11 non-adjustable Fram is listed for all years of 240Z, 280Z, and 280ZX, so I guess they're all swappable.

I found this, not for a Nissan: "use a small slotted screwdriver to turn the adjuster that is located inside of the vacuum fitting. Turn clockwise for earlier shifting, counterclockwise for later shifting."

I guess I need a tough adjustable modulator but guessing and following manufacturer's hype can lead to destruction. I'd like to have an idea what to do before I start "adjusting". Anybody know? Due to the headers it's not real easy to get at the modulator, so would like to get it about right first time.