Switching from Mobil-1 to Castrol GTX
 

Gonna be buying a rebuilt with about 5K on it until I have the money to do a proper rebuild on my 88 NA...

My old engine always had GTX, and it got me 190,000 hard miles, and from what I've read, most people prefer this oil...

The rebuilt I'm buying has always had Mobil-1... Is it cool to just do a straight oil-change from syn to mineral, or do I need to have the engine flushed???

Thanx for any input!!!

as long as there are no noticeable oil sludges/deposits then you can just switch right over.

i like Castrol GTX. good quality oil and best of all is very cheap in price.

i'm guessing what you are saying is that you are buying an already assembled rebuilt engine that has about 5k miles on it? how exactly is he going to check for internal sludges/deposits Mark ;)
i don't think switching over from synthetic to mineral, vice versa, at any mileage will do any harm. i'm not an oil expert, so i can't tell you the specific interactions between mineral and synthetic oil. especially since GTX is a fairly low detergent/additive oil, you will not have any problems.
one thing you could is just to drain all the oil and then you can put a new oil filter and GTX in.

he is gonna reach in the drain and feel around in there for anything that is not liquied

alright, i guess that works :)
however you can only reach so far around in there through the drain plug...but i wouldn't worry about it too much, i can't remember the last time i've seen anything like that come out of an oilpan...