You can buy the block plate (Lakewoood) as a separate line item through all the main wholesale houses, Jegs, Summit, Northern etc... Just get on Lakewood's web site, look up you're application and get their part number... simple as that. This is all assuming that your bellhousing's Lakewood???
Leaving the block plate off increases your input shaft insertion only by 1/8" (still enough to send you to prison in 18 states..
). You'd probably be fine with the 1/8" deeper input depth. That being said, I'd still take comparative measurements to know exactly how much room I have to work with.
Dave