I have done the same to replace the rear main seal. I blocked both sides or the companion way on the deck put a heavy wall inch and a half pipe across and used a chainfall. Removed the forward engine mount nuts, I didn't remove the rear mount nuts. Disconected driveshaft, transmission,bellhousing cleaned every thing did a very careful job with the new seal ( Perkins new seal) Put everything back togeather .I didn't have any leaks in the 4-108 for about fifty hours then the seal started leaking again. Looking back on that project the only thing I would have differenty is to use an after market silacone seal. Allen