I've dp'd as a top several times and it is challenging.
Top#1needs to stay still while top#2gets in there, movement is restricted and pressure in the dick is high, so things get floppy easily. I've never done with a bottome that was so stretched out that it could be done with ease.
In my experience best position is top 1#laying on his back, bottom straddles him and top#2 gets in from above, sort of kneeling over.
99% of the pleasure in this comes from recreating porn / aesthetic appeal / ideas rather than phisical pleasure though.
8 inches sounds long but 1inch diameter is kinda narrow, its likely more comportable. Dicks wont be 100% inside so longer and narrower might work in your favor.
If youre gonna be bottoming take extra care in prepwork- douche, stretch… even use a plug for a while before and poppers might be useful
Best of luck ;D