Well you did say YOU put 20-50 in it. Unless you want to be on here with similar posts I would suggest NOT doing that in the future. Just pull it, rebuild it, and call it a day...well it may take longer than a day.
Ya man, these engines are very reliable and can go EASILY 200+.....IF TAKEN CARE OF....Just take it somewhere, some place that you've been to before, and have the mechanic take a look at it to see whats wrong.......Don't take it to the stealership and Don't let the mechanic do anything until he figures out the problem and SHOWS you whats wrong and gives you a quote.....
It seems like you just want to build your own engine and be done with it, but it's really not that simple.....Either takes a lot of time and knowledge or a lot of $$$.....
First of all you need to get the odometer fixed...sorry I had too and then take it to the mechanic and find out WHY it is smoking, who knows....it could be something really simple and cheap; instead of building a WHOLE OTHER ENGINE....Although, it sounds "simple" to just buy some things and tada(sp?) a new engine....it takes a lot of hard work, dedication, and time......ask anyone who has built one themselves
use 15w/40 oil and add 2 bottle of that stuff, try to drive the car under 35mph for first 50 miles ( 100 miles is wat recomment ). Try that first, it work for me TODAY !!.