Moreton-in-Marsh to York

Yes that dors sound right.
Hopefully our two train experts will roll up with the best combi but if you do a search on the forum its a semi frequently asked question

This question is often asked. A search will give many such threads but 4 hours is about right. There are three basic routes- which you use is personal preference.
1. via London (normally the cheapest, often as fast as the other routes, and arguably the most comfortable trains);
2. switching trains at Worcestershire Parkway and Birmingham New Street;
3. switching trains at Oxford and (usually) Birmingham New Street

If I wasn't wanting to route through London, I personally would prefer Route 2 over Route 3. It is normally cheaper and I prefer the trains used on that route but it's a personal thing.

much as above - it is counterintuitive but south to London, connect Paddington Station by Elizabeth Line (I've come back to correct CrossRail which is what the Elizabeth Line was called when being built, and there will eventually be a CrossRail 2) via Farringdon or just take the Hammersmith & City or Circle Line tubes to Kings Cross and then LNER northbound to York is almost certainly cheaper and easier.