DT125LC Mk1 - tuning

Would be grateful if anyone here can help with the following query;

I am in the process of building a DT125 LC. My frame is a mk1, verified by Yamaha UK who kindly also supplied a Vehicle Registration Number & year of manufacture.

I could not get a DT engine, BUT managed to pick up an RD engine which has dropped straight in, no problem. I have sourced RD electrics, loom etc as I am aware that the mk1 has 6V electrics not 12V & the RD engine will be 12V.

I intend to keep the bike for myself, and to this end it will be made up of the best of the DT bits plus a few other nice custom bits.

I have seen somewhere on here that the standard LC barrel can be bored out to 175 cc... or did I read this incorrectly? I thought I'd seen somewhere that this can be done & that you fit a DT175MX piston? I know that there is an italian big bore kit that appears from time to time, but the costs seem to be prohibitive @ anything from £ 300 - 400. I have no experience of the 125 big bore kits BUT I remember as a spotty youth, most of my mates that ran 50's had either 60 kits, or 80 kits & they did not last 5 mins... mainly knocking out the bottom ends.... Given that my bottom end is good, if I could bore my 125 barrel out to 175cc or fit a big bore, do I need to change the big ends & mains, or will the 125 bottom end take the extra horses that the 175 barrel produces? (I don't want ridiculous power, but would be happy with say 20-25 BHP, rather than the stock 12 BHP)

If I do not go for this option, as I intend to keep the bike for myself, I considered having the barrel tuned by Stan Stephens, as I have a spare. What sort of increase in power can be achieved with a Stage 1 tune? Am I looking at 5 - 10 BHP? And with a Stage 1 tune will it affect the reliability?

Any replies would be appreciated.

Cheers