Quick help with engine #

[Windsor]

I did a breakdown of the #s stamped on my block, but one letter has me drawing a blank. Can't find anywhere that tells me what it means.
PT383R22102315
PT:383:R:2210:2315
Trenton plant:383:?: Wednesday August 16, 1967: serial 2315

Also, I know there are some #s stamped on the crank shaft flange. I could only see 383 stamped when I looked, but will check it tomorrow if I get the trans out. I'm guessing there will be a part # stamped. Can someone tell me where to look to cross reference numbers?

[Alaskan_TA]

R - Regular (fuel)

See the bottom line on the page at http://www.hamtramck-historical.com/images/TSBs/1967/D67-25-1%20p7.jpg

[Windsor]

Thanks. I saw regular fuel mentioned somewhere else too, but it was referring to the model pad on the top, but didnt mention it also being on the one by the starter.