I assume you mean a GLOW engine of 45 size (7.5cc) ?
Simple .... check out Hobby King or any other general online site for 45 - 50 equivalent E-motors ... and the specs.
Direct swap in ..
60A ESC, 4 - 5S LiPo, ~13 - 15" prop ...
Personally I would be using a 5S pack and a 12" prop as a 45 Glow is actually not usually a big prop motor. The glow motor would probably be turning about 10,000 rpm on a 11x7 prop ? So you need to use at least 5S on the E-Motor...
A 60 sized motor if you want to be sure of enough power :
Needs 5 - 7S and 60A ESC, 14 - 17" prop.
Probably too much as the prop to load the motor is too big.