4.1l 250 rebuild help

I bought a 1964 chevy c10 for 1000.00. It has a 4.1L 250 with what the odometer says is 285996 miles on it highly doubt this is correct seeing how I know this is not the original engine I have know idea how many miles are really on it. it runs fine just has a small tap dose not burn oil. but i am going on a deployment soon and am looking to rebuild it when i get back. I was wondering if anyone knows any good places to get a rebuild kit or some performance parts to get a little boost in hp and what is the best manual transmission i can put in it but keeping the 250 as the power plant. Plus any tips any one can give me to help me during the process it would be gratefully appreciated.  

first.. lets ID the motor and possibly the transmission..


sides of the block there should be casting number... usually 6 to 8 numbers.. on a machined flat spot.. possibly near the distributer.. there should be a row of stamping letters and numbers to identify the exact original application of that motor..

you could have almost any of several straight six motors..

post your casting numbers or google them...  V8 numbers are easier to google..

where to get rebuild parts...  there are engine rebuilders all over the place... there are online suppliers all over the place....

because of the age of the motor.. you might want to pick up something like a dial caliper and perhaps a set of teloscopic ID gauges to measure things on the motor..


http://www.harborfreight.com/catalogsearch/result?q=caliper

http://www.harborfreight.com/6-piece-telescoping-gauge-set-5649.html  

well the numbers are D1 7 on its own surface, then CON2 on its own surface then the casting number 377127
                GM
                80
all this is on the same side.