Applying citizenship long term ILR

[Wales27]

Hi this is a great site for information, so hoping maybe someone can advise me on two things, thank you if possible:
I've lived in the UK for 48 years after my American parents moved, they in 1974 had a letter from the home office granting them leave to remain permanently in the UK, my passports always had stamp with given leave to enter the Uk for indefinite period, up till most recent one which with the changeover of added cost and sending away to transfer I was advised to just carry my expired passport for my stamp. I have just passed my Life in the UK test and now am looking at applying for citizenship and getting a british passport but my query is should I use the letter my parents had in 1974(no mention of me or my two brothers one it, though they got citizenship a number of years ago) or just my old passport with stamp on it? My father passed away last year and he dealt with the whole paperwork at the time. The form asks when was granted ILE but I don't know!! I know my parents but not got any paperwork of my own for bar stamp on passport!
My other query is regarding applying with the pilot scheme for passport same time, I understand from guidance that it does not need to be with local NCS office but as I live in Wales and they have separate listing of NCS for Wales, Scotland, England is it still ok to go over the border to do(Cheltenham looks closest that I can see so considering that to save a trip locally and then a trip to Newport for passport interview)? Thank you for any advice and guidance, I've just emailed my brothers too in case they remember what they provided for their citizenship but it's been a long time.

[Wales27]

Just to add to my queries I've just spoken to Cheltenham NCS and looks fine to do pilot there BUT apparently have to attend citizenship ceremony there as well! I was hoping one 220 mile round trip and then local for ceremony, now totally confused as to best way to go ahead-my USA passport runs out shortly so was hoping could complete citizenship and passport application quicker by saving 2 interviews but now not sure if should do citizenship locally and passport separately though I'm 75 miles from passport office anyway. This is such a busy forum but any thoughts would be really grateful, thanks